MEDIUM DUTY MAINTENANCE MANUAL

Electrical System Troubleshooting - T300 18

Introduction NOTE: To succeed in troubleshooting the elec-
trical system of a Kenworth truck, or in adding
This publication is divided into 8 sections. an electrical circuit to a Kenworth truck:

1. Introduction 1. Read and understand “Theory Of Operation” on

page 2, and “Kenworth Electrical System Operation”
2. Theory Of Operation on page 6 before referring to any other sections of
3. Kenworth Electrical System Operation this publication.

4. Wiring Key
5. Electrical Circuit Matrix
6. Tools For Troubleshooting and Repair
7. A Plan For Finding Electrical Malfunctions
8. How To Repair Electrical Malfunctions

(5/3/00) KM718003 Page 1 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Theory Of Operation For alternators equipped with brushes, the rotor is electri-
cally magnetized by a small current flowing through the
The Theory Of Operation is divided into three parts. brushes installed on smooth slip rings. The rotor isn't
magnetized until current actually passes through the
1. Generating Electricity rotor. See Figure 18-2.
a. Alternator
• Voltage
• Current
• Resistance
2. Circuits
a. Series Circuits
• Voltage and Current
b. Parallel Circuits
• Voltage
• Current
• Resistance
3. Series/Parallel Circuits Figure 18-2 Brushes and Slip Rings
a. Circuit Composition For a brushless alternator, current is produced by the
rotor rotating between a stationary magnet and the sta-
Generating Electricity tionary field/stator windings. See Figure 18-3.

Alternator

An alternator produces alternating current that is rectified

into direct current for use in truck circuitry. Some alterna-
tors are equipped with brushes and some are brushless.

Current is produced by rotating a magnet inside a station-

ary winding. The rotating magnet is called a rotor and the
stationary winding is called a stator. See Figure 18-1.

Figure 18-3 Brushless Alternator

Brushless alternators or alternators equipped with

brushes produce alternating current. However, the bat-
tery stores direct current only. A rectifier assembly con-
verts the alternating current to direct current. See Figure
18-4.

Figure 18-1 Rotor and Stator

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Figure 18-5 Water Pressure and Voltage

Current
Figure 18-4 Rectifier Assembly
The flow of electricity through a wire is called current.
A regulator controls the alternator output by adjusting the Without voltage, or pressure, the current will not flow.
magnetic field of the alternator. This regulates the bat- Current is measured in amperes.
tery’s state of charge. See Figure 18-4.
NOTE: Voltage is the electrical pressure that
Electrical current cannot be seen moving. However, a causes the current to flow. Current may be
meter can display the flow of current. A successful tech- thought of as the rate of flow.
nician knows how to read the meters that allow him or her
to diagnose malfunctions and to maintain the electrical Example:
system at maximum operating efficiently. 30 Ibs. of pressure at the water supply will force 150
gallons of water per minute through a fire hose. For
Voltage electricity, let’s say 12 volts at the power supply will
force 30 amperes of electricity through a wire.
Voltage is the electrical pressure that causes the current
to flow. This pressure, measured in volts, is the difference NOTE:
in electrical potential between two points in a circuit.
Voltage = pressure.
The principle for current flow is the same as for water. Current = flow.
Water flows through a hose because there is greater
pressure at the water supply than at the outlet of the Resistance
hose. Current flows through a wire because there is
greater pressure (voltage) at the electrical supply (alter- Resistance to current flow may be thought of as a restric-
nator) than at the component (lamp, motor, etc.). See tion. Resistance is measured in ohms.
Figure 18-5.
Circuits
Basic types of circuits:
• Series Circuit—1 current path.
• Parallel Circuit—2 or more current paths.
• Series/Parallel Circuit—A circuit composed of series
and parallel circuits.

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Series Circuits

A series circuit has 1 current path. The same current

flows through each component. All components oppose
the flow of current. Think of each component as a resis-
tance to current flow. To find total resistance of a series
circuit, add all resistances. If there is a break anywhere in
the circuit, no current will flow. See Figure 18-6.

Figure 18-7 Parallel Circuit

Figure 18-7 shows a parallel circuit with 2 current paths,

Figure 18-6 Series Circuit
I1 and I2. To find the total current IT in the parallel circuit,
Voltage and Current add the current in I1 and I2.

In a series circuit, the same current flows through all I1 + I2 = IT

components. How much current is determined by the
voltage supply and total resistance of the circuit compo- Voltage
nents.
In a parallel circuit, all branches are connected in parallel
NOTE: The more the resistance, the less the with the power supply. The voltage produced by the
current flow. The less the resistance, the more power supply is the same at each branch.
the current flow.
Current

Parallel Circuits In a parallel circuit, current flowing through each branch

is determined by the resistance.
A parallel circuit has more than one path for current flow.
See Figure 18-7. In a branch:
High resistance = low current. Low resistance = high
current.

As branches are added:

Total resistance decreases. Total circuit current
increases.

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Electrical System Troubleshooting - T300 18
Resistance NOTE:

Resistance is measured in Ohms Total resistance in a • A series circuit has 1 current path.
parallel circuit is less than the least branch resistance.
• A parallel circuit has 2 or more current paths.
Example: • A series/parallel circuit is composed of series
See Figure 18-8. and parallel circuits.

See Figure 18-9 and Figure 18-10.

If the branch with least resistance (R1) is 3, total resis-
tance will be less than 3. Refer to formula for determining
resistance.

Figure 18-9 Series/Parallel Circuit

Figure 18-8 Resistance

Series/Parallel Circuits
Figure 18-10 Series/Parallel Circuit
Circuit Composition

A series/parallel circuit consists of both types of circuits,

series and parallel.

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Kenworth Electrical System • Circuit function.

Operation • Circuit number of all wires in a circuit.

• Color of all wires in a circuit.
How To Read A Wiring Diagram and Wiring • Destination of wire or purpose of circuit.
Key • Location of:
A wiring diagram is a map of symbols for an electrical cir- – Terminals
cuit. To succeed in understanding the operation of Ken- – Splices
worth’s electrical system, a technician must be able to – Plugs
read a Kenworth wiring diagram and wiring key. A dia- – Grounds
gram and wiring key will show:
• Relation of components on chassis in Cab and Chas-
sis wiring diagrams.

Wiring Key Example: G 27 SU-A µ

Wiring Code Definition List Function. . . . . . . G = Gauge

Circuit
Example: P 18 BZ-XXX
Number . . . . . . . 27 = Aux. Trans. Oil Temp.
P -- Function See Function De- Destination or
scription Below. Purpose . . . . . . . SU = Sending Unit
18 -- Circuit Number See Circuit Descrip- Distinction
tion on page 7 between different -A = A, B, C...etc.
through page 11. circuits with the
same circuit
BZ -- Destination or See Description on number . . . . . . .
Purpose page 11.
Vendor
XXX -- Vendor Reference Reference . . . . . µ = For Vendor use only

Explanation:

G27SUA- µ = Aux. Trans. Oil Temp. Gauge Wire to Send-

FUNCTION ing Unit
LETTER DESCRIPTION
C Components Wiring Code, Spare Circuit Breaker

E ECU / Electronic Control Example: PCB 33-XXX

G Gauges
PCB -- Function Power from Spare
GND Ground Circuit Breaker.
H Heating / Air Conditioning 33 -- Circuit Breaker Tells location of cir-
L Lighting Number cuit breaker.

P Power XXX -- Vendor Reference For vendor use

only
R Relay
S Spare See “Cab Heater and A/C Wiring Diagram” on page 17
for example wiring diagram and wiring symbols.

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Electrical System Troubleshooting - T300 18
Wiring Circuits Circuit
Circuit Description Color Code
No.

Circuit 31. Clutch Position Yellow/Purple

Circuit Description Color Code
No.
32. Service Brake Sense Yellow/Green
Gnd Ground ATA White
33. Left Front Directional Signal Lamp Yellow/Black
1. Tail and Park Lamps ATA Brown
34. Right Front Directional Signal Lamp Green/Black
2. Stop Lamps ATA Red
35. Left Rear Directional Signal Lamp ATA/Yellow
3. Marker & Clearance Lamps ATA Black
36. Right Rear Directional Signal Lamp ATA/Green
4. Hot Wire for AuxiliaryDevices on Trailer ATA Blue
37. Idle Validation Off Brown/Black
5. Head Lamps Lt. Blue
38. Idle Validation Signal Yellow/Red
6. Low Beam Red/Black
39. Hot Feed Line to Pressure Auxiliary Switch Red/Pink
7. High Beam Blue/White
40. Return Line from Pressure Auxiliary Switch Red/Violet
8. Control Circuit for Accessory Relays Red/Gray
41. Sanders Brown/White
9. LH Road or Fog Lamp Purple
42. Radio Receiver Green/Red
10. RH Road or Fog Lamp Purple/White
43. Radio Transmitter Green/Orange
11. Horn Relay Ground White/Green
44. Differential Lock Lt. Blue/Brown
12. Horn Relay Hot Green/White
45. Fifth Wheel Lock Brown/Green
13. Panel Lamps Gray
46. Low Air Green/Tan
14. Flood or Loading Lamp Red/Tan
47. Two Speed Axle Yellow/Blue
15. Battery Charging Gray/Yellow
48. Idle Increment Red/White
16. Post Spot Lamp Gray/Red
49. Idle Decrement Red/Black
17. Starter Solenoid Orange
50. Circuit Breaker to Terminal Strip Pink/Blue
18. Hot Line to Buzzer and Warning Devices Lt. Green
51. Accessory Term. of Ignition Switch to Circuit Red/Yellow
19. Starter Switch to Solenoid Tan Breaker

20. Windshield Washer Motor Lt. Blue/Yellow 52. Ignition Circuit Breaker to Accessories White/Black

21. Battery to Ammeter - Main Charge and Dis- Black 53. Horn Relay to Horn Pink/Black
charge Line
54. Acc. Circuit Breaker to Accessories White/Red
22. Regulator Battery Term to Ammeter Charging Black
Line 55. Check Engine Light Blue/Yellow

23. Ether Start Tan/Green 56. Low Coolant Lt. Green/Blue

24. Engine Heater Blue/Pink 57. Electric Water Temp. Purple/Yellow

25. Engine Oil Temperature Pink 58. High Water Temp. Low Oil Press. Green/Brown

26. Main Trans. Oil Temp. Violet 59. Remote Throttle Enable Tan

27. Aux. Trans. Oil Temp. Gray/Black 60. Remote Throttle Signal Input Grey/Pink

28. First or Single Rear Axle Temp. Gray/Black 61. Ground White

29. Second Rear Axle Temp. Gray/Black 62. Defroster Fan Yellow/Red

30. Heater - Pass. Side Lt. BLue/Black 63. Switched tri-state Derate Grey/Lt Blue

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Electrical System Troubleshooting - T300 18

Circuit Circuit
Circuit Description Color Code Circuit Description Color Code
No. No.

64. Turn Signal Feed Orange/Blue 96. Engine Brake Half (Low/Hi) Lt. Green/Yellow

65. Courtesy Lamps Pink/Green 97. Engine Retard Switches Lt. Blue/Green

66. Dome Lamp - Front Violet/White 98. Engine Brake Full (Med/Hi) Lt. Green/Black

67. Dome Lamp - Sleeper Tan/Yellow 99. Fuel Heater or Filter Lt. Green/Red

68. Voltage Regulator Energizing Control Line Red/Blue 100. Interaxle Diff. Lock Indicator Lamp White/Red

69. Switch Common Grey 101. General Purpose Exterior Lamps Green/Lt Blue

70. Turn Signal Flasher to Switch Volt Reg. or Yellow/Green 102. Air Conditioner Clutch Control Lt. Green/White
Press. Switch
103. Spare Relay Power Contact - Normally ClosedBlue
71. Windshield Wiper Black/Green
104. Spare Relay Power Contact - Normally Open Blue
72. Fuel Gauge Tan/Black
105. Spare Relay Power Contact - Common Blue
73. Fuel Gauge - LH Tank with Two Senders Tan/Red
106. Spare Relay Coil (+) Blue
74. Fuel Pressure Orange/Green
107. Spare Relay Coil (-) Blue
75. LH Windshield Wiper Black/Green
108. J1587/1706 Data Link Bus + Blue/Black
76. RH Windshield Wiper Green/Black
109. J1587/1706 Data Link Bus - Blue/Lt. Blue
77. Sleeper Heater Blue/Orange
110. DRL Power Brown/Lt Blue
78. Sleeper Relay Controls to Sleeper Heater Blue/Gray
Motor 111. DRL Sense Orange/Black

79. Backup Lamp Pink/White 112. Remote PTO Enable Black/White

80. Sign Lamp Red/Orange 113. Feed from Ignition Term. of Key Switch to Cir-Red/Brown
cuit Breaker
81. Clean Power Red/Lt Blue
114. Adlo System Tan/White
82. Cab Feed Line Between Circuit Breakers and Orange/Red
Key Switch 115. Alt. Sensing Circuit (Regulator Term or 1 of 3 Black/White
Alt. AC Terms)
83. Mirror Motor Brown/Tan
116. Sleeper Accessories and Cigar Lighter Pink/Red
84. Starter Relay Feed Black/Orange
117. Charging Circuit - Alternator to Ammeter Red
85. Reversible Motor - Up or Forward Lt. Blue/Tan
118. Cummins to PT Pump; 8V-71 & Cat. to Fuel Red/Green
86. Reversible Motor - Down or Reverse Tan/Lt. Blue Shutdown

87. Air Conditioning or Cooler Yellow/White 119. Shunted Ammeter Brown

88. Glow Plug Orange/White 120. Diagnostic Conn Battery Power Red/Blue

89. Mirror Heat Brown/Yellow 121. Diagnostic Test Switch Yellow

90. Expeller Valve - Air Tank Heat - Air Dryer Purple/Red 122. Alternator Warning Lamp Lt. Green/Orange

91. VARASHIELD Indicator Lt. Blue/Red 123. Sleeper Air Control Red

92. VARASHIELD Down Tan/Lt. Blue 124. Sleeper Box Air Conditioning Control Circuit Lt. Green/White

93. VARASHIELD Up Lt. Blue/ Tan 125. Park Brake Sense for DRL Lt. Green/Yellow

94. Transmission Lockup Green/Pink 126. Batt. Ckt. Breaker - DRL Red/Violet

95. Engine Retard Black/Lt. Green 127. Throttle Power Brown/Grey

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Circuit Circuit
Circuit Description Color Code Circuit Description Color Code
No. No.

128. Throttle Sense Position Brown/Red 161. Anti-Lock Solenoid, Right Front Axle Orange/Yellow

129. Throttle Position Brown/Green 162. Anti-Lock Solenoid, Left Rear or Left Forward Violet/Green
Rear Axle
130.
163. Anti-Lock Solenoid, Right Rear or Right For- Violet/Blue
131. C.B. Speaker Wiring (-) White/Grey ward Rear Axle

132. C.B. Speaker Wiring (+) Brown/Grey 164. Anti-Lock Solenoid, Left Rear Rear Axle Violet/Orange

133. Radio Speaker Ground Circuit RH Speaker Orange/Gray 165. Anti-Lock Solenoid, Right Rear Rear Axle Violet/Yellow

134. Radio Speaker Ground Circuit LH Speaker Gray/Orange 166. Anti-Lock Wheel Speed Sensor, Left Front Yellow/Black

135. Radio RH Speaker Circuit (Sleeper) Green/Gray 167. Anti-Lock Wheel Speed Sensor, Right Front Yellow/White

136. Radio LH Speaker Circuit (Sleeper) Gray/Lt. Green 168. Anti-Lock Wheel Speed Sensor, Left Rear or Yellow/Orange
Left Forward Rear
137. Radio RH Speaker Circuit (Cab) Black/Gray
169. Anti-Lock Wheel Speed Sensor, Right Rear Yellow/Blue
138. Radio LH SpeakerCircuit (Cab) Gray/Green
or Right Forward Rear
139. Cruise On/Off Orange/Brown
170. Anti-Lock Wheel Speed Sensor, Left Rear Yellow/Lt. Green
Rear
140. Cruise Set Orange/Green
171. Anti-Lock Wheel Speed Sensor, Right Rear Yellow/Tan
141. Cruise Resume Orange/Red
Rear
142. J1922 Data Link + Yellow
172. Anti-Slip Solenoid Orange/Purple
143. J1922 Data Link - Orange
173. ECU/Electronic Control Switched Circuit Gray/Blue
144. Fan Clutch Control White/Lt. Green
174. Motor Common Mirrors White/Brown
145. Dump Gate Front White
175. Power Mirrors Left/Right White/Orange
146. Dump Gate Rear White
176. Power Mirrors Up/Down Grey/Violet
147. Torque Limiting Circuit, PT Pump to Pressure Red/Green
177. Power Windows Up Grey/Lt Blue
Switch
178. Power Windows Down White/Lt Blue
148. Electric Tach. Sending Circuit Black/Red
179. Power Windows Common White/Tan
149. Hobbs Hour Meter Gray/Yellow
180. Power Door Locks White/Purple
150. Electric Speedo Sending Circuit Blue/Red
181. Auxilliary Battery Red
151. Smart Sensor Yellow/Violet
182. Proprietary Bus (-) Grey/Red
152. Check Fluids Lamp Green/Orange
183. Proprietary Bus (+) Red/Grey
153. Anti-Lock Brake System Monitor Feed Pink/Purple
184. CB & AM/FM Radio Power Lt Green/Pink
154. Anti-Lock Brake System Power Purple/Pink
185. J1939 Data Link (High) Yellow
155. Anti-Lock Brake System Warning - Fail CircuitViolet/Brown
186. J1939 Data Link (Low) Green
156. Anti-Lock Brake System Diagnostic Circuit Brown/Violet
187. J1939 Data Link (Shield) White
157. Pyrometer (Australia only) Green
188.
158. Check Engine Lamp Brown/Orange
189.
159. Stop Engine Lamp Brown/White
190. Door Lock Actuator Feed Wire “B” Blue/Red
160. Anti-Lock Solenoid, Left Front Axle Orange/White

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Electrical System Troubleshooting - T300 18

Circuit Circuit
Circuit Description Color Code Circuit Description Color Code
No. No.

191. Door Lock Actuator Feed Wire “A” Green/Red 225. not used

192. Door Unlock Black/Red 226. Engine Governor Switch Orange/Blue

193. Door Lock White/Red 227. not used

194. Door Unlock Relay Ground Brown/Red 228. Collision Warning Power Red/Purple

195. Door Lock Relay Ground Black/Red 229. Collision Warning Bus Positive Orange/Lt Blue

196. Air Bag Warning Lamp Blue/Yellow 230. Collision Warning Bus Negative Black/Tan

197. Air Bag Battery Power Red/Yellow 231. Collision Warning Side Sensor Power, Primary Red/Lt Green

198. Air Bag Ignition Power Orange/Yellow 232. Collision Warning Side Sensor Ground, Primary Violet/Lt Green

199. Air bag Firing Circuit Yellow/Pink 233. Collision Warning Side Sensor Signal, Primary Purple/Lt Green

200. Seat Belt Switch Yellow/Brown 234. Collision Warning Side Sensor Power, Secondary Red/White

201. Aux Input Gray/Green 235. Collision Warning Side Sensor Ground, Secondary Violet/White

202. Aux Output Gray/Yellow 236. Collision Warning Side Sensor Signal, Secondary Purple/White

203. Transmission Shift Modulation Purple/Lt Blue 237. Collision Warning Driver’s Display Unit PowerPurple/Tan

204. Transmission In Gear Pruple/Green 238. Collision Warning Side Sensor Display Signal, Green/Purple
Primary
205. Low Coolant Low Blue/Black
239. Collision Warning Side Sensor Display Signal, Gray/Purple
206. Low Coolant High Blue/White Secondary

207. +5 VDC Blue/Red 240. Collision Warning Front Sensor Power Red/Yellow

208. Return Blue/Green 241. Collision Warning Front Sensor Ground Violet/Yellow

209. not used 242 not used

thru
210. Maintenance Indicator Lamp Green/Red 300.

211. Water-In-Fuel Indicator Lamp Green/Yellow 301. Spare Circuit Black/White

212. Proprietary Can Bus (High) Red 302. Spare Circuit Black/Yellow

213. Proprietary Can Bus (Low) Black 303. Spare Circuit Black/Red

214. Proprietary Can Bus (Shield) White 304. Spare Circuit Black/Green

215. PTO Lamp Brown/Blue 305. Spare Circuit Black/Orange

216. Remote PTO Set Brown/Lt Green 306. Spare Circuit Black/Lt Blue

217. Remote PTO Resume Brown/Yellow 307. Spare Circuit Black/Pink

218. not used 308. Spare Circuit Brown/Blue

219. Input Sensor Common #1 White/Purple 309. Spare Circuit Brown/Lt Blue

220. Input Sensor Common #2 White/Orange 310. Spare Circuit Brown/Lt Green

221. Trans Shift Solenoid Tan/Purple 311. Spare Circuit Lt Blue/Gray

222. Trans Position Sensor Tan/Lt Green 312. Spare Circuit Brown/Yellow

223. Auto Trans Manual Override Tan/Blue 313. Spare Circuit Lt Blue/Lt Green

224. not used

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Circuit
Circuit Destination or Purpose
Circuit Description Color Code
No.
AL Alternator
314. Spare Circuit Lt Blue/Orange AM Actuator Motor

315. Spare Circuit Lt Blue/Pink AO Automatic Override

AR Acc. Relay
316. Spare Circuit Lt Blue/Purple
AT Air Tank
317. Spare Circuit Lt Blue/Gray
AU Automatic
318. Spare Circuit Lt Blue/White
AX Auxiliary
319. Spare Circuit Lt Green/Purple AXL Auxiliary Left

320. Spare Circuit Lt Green/Brown AXR Auxiliary Right

AXT Axle Temperature

ACC Spare Accessory Circuits Yellow B

ALTI Alternator “I” Terminal Feed Black BB Bus Bar
BL Backup Lamp
BAT Spare Battery Circuits Red
BR Breaker
CAP Noise Suppressing Capacitor Yellow/Grey
BS Binary Switch
ERET Electronic Return White/Pink
BZ Buzzer
GND Ground (ATA) White

IGN Spare Ignition Circuits Orange

C
OAT1 Outside Air Temperature (+) White/Violet
CA Collision Warning
OAT2 Outside Air Temperature (-) White/Yellow CB C.B. Radio
PCB Spare Power Circuit Breakers Black CC Charging Circuit

PWR Battery (+) Red CCT Cruise Control

CG Cigar Lighter
RET Instrument Return White/Blue
CH Cab Heater
SPC Spare PassThrough Chassis Circuits Blue/Tan
CK Clock
SPE Spare PassThrough Engine Circuits Brown/Pink CL Clearance Lamps
SPR Spare PassThrough Roof Circuits Pink CM Common

SPS Spare PassThrough Sleeper Circuits Yellow/Lt Blue CP Clean Power

CS Clutch SW
V 24 Volt Charging Wire White
CT Control
CTS CTIS

Circuit Destination or Purpose D

DB Data Bus
A DC Door Courtesy Lamp
ABS Anti-Lock Brakes DCL Door Courtesy Left
AC Air Conditioning DCR Door Courtesy Right
AD Air Dryer DF Defroster Fan
AF Accessories Feed DG Diagnostic
AH Aux. Heater DK Door Lock

(5/3/00) KM718003 Page 11 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Circuit Destination or Purpose Circuit Destination or Purpose
DL Diff Lock HN Horn
DM Dome Lamp HP High Pressure
DMF Dome Floor HS Heat Sensor
DML Dome Left HW High Water - Low Oil
DMR Dome Right
I
DRL Daytime Running Lamp
IGB Ignition Bus Bar
DS Dimmer Switch
D1 Diagonal 1 (Antilock)
J
D2 Diagonal 2 (Antilock)
JB Jacob’s Brake
JF Jacob’s Brake Full
E
JH Jacob’s Brake Half
EF Engine Fan
EG Engine Gauge
K
EH Engine Heater
KS Key Switch
EM Engine ECU
ER Engine Retard L
ES Ether Start LA Low Air
EV Expeller Valve LB Low Beam
LC Low Coolant
F
LH Low Heat
FC Freon Compressor
LI Lights - Instrument
FF Fuel Filter
LO Low Oil
FG Fog Light
LP Low Pressure
FH Fan Hub
LT Left Turn
FL Flood Lamp
LV Left Valve (ASR)
FL2 Flood Lamp, 2nd Set
LW Low
FP Fuel Pressure
FT Fuel Tank Heater M
FW Fifth Wheel Lock MH Mirror Heat
ML Marker Lamp
G
MM Motorized Mirror
GA Gauge
MN Manual
GD Gear Display
MO Manual Override
GP Glow Plug
MR Motor
MT Medium Temp
H
MW Multiplex Wheel
HB High Beam
HC Horton Fan Clutch
N
HH High Heat
NC Normally Closed
HI High
NO Normally Open
HL Headlamps
NS Neutral Start
HM Hobbs Hour Meter

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Electrical System Troubleshooting - T300 18
Circuit Destination or Purpose Circuit Destination or Purpose
SP Speedometer
P
SR Starter
PB Park Brake
SS Sleeper Speaker
PI Position Indicator
ST Stop Lamp
PL Park Lamps
SU Sending Unit
PTO PTO
SV Solenoid Valve
PW Power Window
SW Switch
PWB Power Bus Bar
PWL Power Windows, Left T
PWR Power Windows, Right TC Tachometer
PY Pyrometer TCT Traction Control
TK Trip Tracker
R
TL Tail Lamp
RC Roof Condenser
TM Terminal Strip
RCC Rear Vision Camera
TN Turn Signal
RD Rear Directional LP
TR Trailer
RF Refrigerator
TRE Transmission ECU
RL Road Lamp
TRS Transmission Shifter
RM Radio Memory
TS Throttle Switch
RP Radio Power
TV Television
RR Radio Receiver
RS Radio Speaker
RT Right Turn U
RV Right Valve (ASR) US Unitary Switch

RY Relay USW Unswitched

S V
S Splice VR Voltage Regulator

SA Sleeper Accessories VS VARASHIELD

SC Sleeper Control
W
SD Engine Shutdown
WD Wiper Delay
SG Safety Gauges
WL Warning Lamp
SH Sleeper Heat
WM Wiper Motor
SI Solenoid Valve - Inlet
WS Wheel Sensor
SL Spot Lamp
WW Windshield Washer
SN Sign Lamp
SO Solenoid Valve - Outlet REF: R076-3315, Rev N

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Electrical System Troubleshooting - T300 18

BAT CIRCUITS ACC CIRCUITS IGN CIRCUITS

MARKER LP TAIL LP 1 20
RELAY RELAY 15 30 29 10
BRAKE SW, TURN
SIGNAL/HAZARD HEATER A/C BACKUP LP/ ALARM
5 10 15
DOME/ GAUGES SHUTDOWN
COURTESY LPS
3 15 17 10 31 10
HIGH BEAM HORN HORN RADIO WARNING LPS
RELAY RELAY
4 20 18 20 32 15
CIGAR LIGHTER WIPER/WASHER ENGINE FAN
5 15 19 5 33 10
TAIL LAMPS DRL ENG PRE-HT
LOW BEAM HEATER-A/C 15 15 10
RELAY RELAY
MARKER LAMPS AIR DRYER SPARE-SP3
7 20 21 5 35 15
HDLTS-LOW BEAM MIRROR HEAT ELEC. TRANS.
8 20 22 5 36 5
DIM SW HDLTS-HI BEAM FUEL/WATER SEP ABS-ECU
RELAY
HAZARD/ 10 5 15
TURN SIGNAL
FLASHER DIAGNOSTIC CONN. CB RADIO ABS-TRAILER
10 5 24 10 38 15
RADIO MEMORY ENG BRAKE ABS DIAG-1
MIRROR 11 15 25 15 39 15
HEAT
DRL SPARE-SP1 ABS DIAG-2
12 15 26 15 40 10
MIRROR HEAT SPARE-SP2 FLOOD LAMP
FUEL/WATER 15 20 15
SEPARATOR
EXHAUST RELAY FUEL/WATER SEP RH PWR WINDOW SPARE-SP4
BRAKE
ABS 14 10 28 10 42 10
TRLR HOTLINE GAUGE LAMPS SPARE-SP5

Figure 18-11 Typical Fuse Panel Layout

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Electrical Circuit Matrix 3. Circuit is identified by the number at intersection of
stripe column and solid color row.
To identify circuit number:
Example:
1. Find solid color of wire in the row at the top of the
What is the circuit number of an orange wire with a
page.
red stripe?
2. Find stripe color of wire in the column at the left of
1. Find Orange in the solid color row.
the page.
2. Find Red in the stripe column.
NOTE: A red wire with a red stripe is a solid red
wire. A black wire with a black stripe is a solid 3. Red and Orange intersect at circuits number 82 and
black wire, etc. 141.
Stripe Solid Color
Lt. Lt.
Black Blue Brown Green Gray Orange Pink Purple Red Tan Violet White Yellow
Blue Green
Black 3, 21 108 37 34 27 30 98 111 53 6 72 52 33
22 76 28 49 166
ALTI 29
PCBXX
Blue 4, 103 215 173 56 64 50 68 163 RET 47
104 308 226 120 169
105
106
107
Brown 1,119 58 44 320 139 113 155 174 200
Green 71 208 45 36 138 97 74 65 204 118 23 162 11 32
75 129 157 140 147 70
304 186
Gray 137 78 127 135 13 311 317 133 8 131 CAP
132 69 183
Lt. Blue 306 109 110 101 63 5 203 81 86 178 SPS
309 177 92
Lt. Green 95 205 216 136 313 18 144 170
310
Orange 84 77 158 43 134 314 122 17 80 164 175 168
305 152 143 220
IGN
Pink 307 24 SPE 94 60 315 184 25 154 39 ERET 199
SPR
Purple 316 319 172 153 9 180 31
219
Red 148 150 128 42 16 91 99 82 116 90 2, 117 73 54 38
192 190 194 191 182 141 123 100 62
195 207 210 181 193
303 BAT
Tan SPC 63 46 93 14 19 179 171
85 59
Violet 156 176 40 26 OAT1 151
126
White 112 7 159 12 318 124 160 79 10 48 114 66 146 167
115 206 41 102 88 61 87
301 V
GND
145
187
Yellow 302 55 89 211 149 20 96 161 57 51 67 165 OAT2 35
196 217 15 125 198 197 121
312 142
ACC
185

(5/3/00) KM718003 Page 15 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
In Figure 18-12, the example is of a wire with a code of
P30CH. Break the code into three parts:
Function
Circuit Description Description
1 2 3 Letters

. .
P 30 CH . .
30 Heater - Pass. Side Lt. Blue/Black
1P Identifies the circuit function. .
. .
Turn to the Wiring Key on page 6. Find the letter P in the . .

list of function letters.

The number 30 is a light blue wire with a black stripe that
is the power circuit to the heater.
Function
Description 3 CH Identifies the Destination or Purpose.
Letters

. . Turn to the Circuit Destination or Purpose on page 11.

. .
P. . . . . . . . . . . . . . . Power
Find CH in Section W.
. .
. . C
. . CH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cab Heater

The letter P stands for Power. P30CH is a power circuit. CH is identified as a Cab Heater.
2 30 Identifies the circuit number of the wire. Code P30CH means that this is a power circuit with a
light blue wire with a black stripe that supplies power to
Turn to the Wiring Circuits on page 7. Find Circuit No. 30 the cab heater.
in the list of circuits.
NOTE: In this case, the circuit supplies power
to the fan motor.

Follow this method to identify all wiring codes in Ken-

worth wiring diagrams.

Page 16 of 44 KM718003 (5/3/00)

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

12
HEATER - A/C
RELAY
A/C EXT SW
HARNESS
C102FC BINARY
10 LT GRN/WHT PRESSURE
C SWITCH
RELAY 16
A/C EXT
2 INSTR ENG HARNESS
INSTR HARNESS HARNESS
ACC CKT HARNESS 11
ENG

GND LT GRN/WHT
ACC 10 AMP HARNESS

C102FA
FUSE P30CH C102FC C102FC
NO. 1 P82
KSA LT BLU/BLK LT GRN/WHT LT GRN/WHT
GND ENG
WHT
HARNESS

WHT
14
RESISTOR ENG GND
MOUNTED IN HARNESS
LT GRN/WHT

MAIN DUCT 13
LT BLU/BLK

ENG
CLUTCH
R102FC
P30CH

GROUND

RESISTOR
5 A/C COMPRESSOR
HTR CLUTCH

BRN LOW
RED
HARNESS
BLK
HI

MED

GND
INSTR WHT
HARNESS P30CH LOW
9
LT BLU/BLK MED RED
GND INSTR HEATER BRN
LT GRN/WHT

LT BLU/BLK

HARN HARNESS HI
CAB
P30CH

BLK
R102FC

HEATER FAN
GROUND 3 HARNESS SWITCH
6 HEATER-A/C
CONTROL ASSY
R102SW
L13LI L13LI LT GRN/WHT
GRY GRY
NC 15
BLK

HEATER NO
HI

HARNESS COM
INSTR HEATER
HARNESS 7 COMPRESSOR PANEL
LT BLU/BLK

HARN
CLUTCH SW LIGHT
LT GRN/WHT P30CH

4
GENERAL NOTES:
1) USE ON MODEL T300.
LT GRN/WHT R102SW

2 5-WAY MINI ISO RELAY SOCKET POS. NO. 2

OF PWR DIST CTR IN CAB.
3 4-WAY PACKARD M/P 280 UNSEALED CONN IN CAB,
BEHIND DASH, CENTER SECTION.
4 3-WAY PACKARD M/P 280 UNSEALED CONN IN CAB,
R102FC

BEHIND DASH, CENTER SECTION. HI

5 3-WAY PACKARD 56 SERIES CONN IN CAB BLK
BEHIND DASH AT RESISTOR ASSEMBLY. P30CH
6 4-WAY PACKARD M/P 280 UNSEALED CONN IN CAB, R102SW LT BLU/BLK
BEHIND DASH, AT HEATER-A/C CONTROLS. R102FC LT GRN/WHT
7 3-WAY PACKARD M/P 280 UNSEALED CONN IN CAB, LT GRN/WHT
BEHIND DASH, AT HEATER-A/C CONTROLS.
8 4-WAY PACKARD M/P 280 UNSEALED CONN IN CAB,
BEHIND DASH, AT HEATER-A/C UNIT. HEATER
HARNESS
9 1-WAY RING TERM CONN IN CAB, AT FIREWALL
GND STUD. 8
10 22-WAY PACKARD WEATHER PACK BULKHEAD CONN
ON FIREWALL, RIDERS SIDE.
11 4-WAY PACKARD M/P 280 SEALED CONN ON RH
SIDE OF ENG NEXT TO A/C COMPRESSOR.
12 2-WAY PACKARD M/P 150 SEALED CONN AT BINARY
PRESS SW ON SIDE OF CONDENSOR IN HOSE FTG.
13 2-WAY PACKARD M/P 280 SEALED CONN ON RH
SIDE OF ENG AT A/C COMPRESSOR. M
14 1-WAY RING TERM CONN ON LH SIDE OF
ENG AT GND BOLT. THERMOSTAT FAN
15 COMPRESSOR CLUTCH SWITCH IS IN THE NORMALLY- SWITCH (N.C.) MOTOR
CLOSED (N.C.) POSITION WHEN IN A/C, BI-LEVEL,
OR DEFROST MODE. HEATER-
16 BINARY PRESSURE SWITCH IS NORMALLY-OPEN PRIOR A/C UNIT
TO INSTALLATION. AFTER INSTALLATION THE SWITCH
IS CLOSED DUE TO NOMINAL REFRIGERANT PRESSURE,
AND OPENS AT LOW & HIGH PRESSURE SETPOINTS.
REF: R115-5633

Figure 18-12 Cab Heater and A/C Wiring Diagram

(5/3/00) KM718003 Page 17 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
The Cab Htr/AC wiring diagram is one of the most com- The power circuit from the Accessory Buss Bar to the
plex in the electrical system. If the operation of this elec- coil is P30CH. The circuit is a light blue wire with a
trical system is understood, understanding the other black stripe.
systems and diagrams should be simple.
NOTE: For an explanation of wire codes, see
In Figure 18-12, trace the current path in the circuit that “Wiring Key” on page 6.
actuates the A/C Compressor Clutch.
With the key switch turned to ON, current travels:
1. Find the A/C Compressor Clutch on the wiring dia-
11. From the splice to :
gram.
• The switch common of the Cab A/C relay
2. Tracing from the A/C Compressor Clutch to the
source of power, find circuit C102FA. The circuit is a • To coil of the Cab A/C relay
light green wire with a white stripe. From the coil of the Cab A/C relay, current travels:
3. From the A/C Compressor Clutch, circuit C102FA 12. Through circuit R102FC. The circuit is a light green
travels through the connector for the A/C Compres- wire with a white stripe. It goes through a 3-way con-
sor Clutch/Engine Harness. nector to the Instrument Harness/Heater Harness.
4. To a 4-way connector for the Engine Harness/A/C
NOTE: The notes on the wiring diagram, near
Extension Harness
the connector, indicate the connector color,
NOTE: Look for a black connector located on type, and location.
the right side of the engine near the A/C Com- 13. To a 4-way connector at the Heater-A/C unit.
pressor.
14. Through the Thermostat Switch.
5. To the Binary Pressure Switch.
15. Back through the 4-way connector Heater-A/C
6. From the Binary Pressure Switch, circuit C102FC unit/Heater Harness. The circuit changes to R102SW
travels back through the 4-way connector to the but keeps the same color light green wire with a white
Engine Harness. stripe.
7. To a 22-way bulkhead connector on the cab side of
the firewall for the Engine Harness/Instrument Har- NOTE: The wire color of a circuit is determined
ness. from the circuit number, not the prefix or suffix of
the circuit number.
8. To the Cab A/C relay in th4e Power Distribution Cen-
ter (which is behind the dash panel to the left of the 16. To a 3-way connector at the Heater-A/C Control
glove box. Assembly.

9. To trace the current path in the circuit that actuates 17. Through the Compressor Clutch Switch in the
the Cab Air Conditioning Relay, find the power circuit Heater-A/C Control Assembly.
connected to the relay.
NOTE: The Compressor Clutch Switch is in
the normally-closed (N.C.) position when in
NOTE: A relay has 2 major components:
A/C, Bi-Level, or Defrost modes.
•A switch.
18. Then to the Fan Switch in the Heater-A/C Control
•A coil. Assembly.
Current passing through the coil actuates the 19. It travels through the switch common when the Fan
switch. To find the power circuit that actuates a Switch is in either Low, Medium, or High position
relay, find the circuit that actuates the coil. through the 4-way connector Heater-A/C Control
10. Tracing from the coil of the relay to the source of Assembly/Heater Harness.
power, find the amp fuse on the Accessory Buss Bar. 20. Back to the Instrument Harness through the 4-way
connector and then to the Cab Ground completing
NOTE: The Accessory Buss Bar has power
the circuit which activates the A/C Compressor
only when the key switch is in the ON or
Clutch.
ACC (Accessory) position.

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Electrical System Sub-Systems Cranking System Operation

Kenworth’s heavy-duty electrical system is composed of Cranking system operation is very much alike for different
three sub-systems. Kenworth vehicles. Follow the description of cranking
operation by referring to the proper wiring diagram.
1. Cranking System
2. Charging System Charging System

3. Accessories The Charging System contains the:

Cranking System • Alternator

• Voltage Regulator—may be component of alternator.
The Cranking System contains the:
• Battery
• Cranking Motor
• Cranking Motor Solenoid—mounted on the cranking Alternator
motor.
The alternator produces alternating current which is con-
• Keyswitch verted to direct current by a diode assembly.
• Starter Relay
Voltage Regulator
• Wires and Cables
The voltage regulator controls the alternator voltage,
• Batteries
maintaining constant voltage with changing loads.

Battery

The battery stores electrical energy in a chemical state.

Wires and Cables

Wires and cables transfer electrical current between

components in the charging system.

(5/3/00) KM718003 Page 19 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Tools For Troubleshooting and Repair Improper meter connections will provide false measure-
ments and could damage the meter.
1. Tools For Troubleshooting
A meter is connected to a circuit by means of the termi-
a. Wiring Diagrams
nals on the meter. The meter terminals are permanently
b. Meters: connected to the jacks on the meter case. Connect test
leads to the jacks when the meter is in service. Observe
• Voltmeter
polarity markings (+ and—) on the meter when connect-
• Ammeter ing the meter to the circuit. Common color markings indi-
cate a red jack for positive and a black jack for negative.
• Ohmmeter
See Figure 18-13.
• Multimeter—combines a voltmeter and ohmme-
ter.
c. Hydrometer
d. 12 Volt Test Light
e. Self-Powered Test Light
2. Tools For Repair
a. Screwdrivers
b. Wrenches or Nutdrivers
c. Sidecutters
d. Wire Strippers

Figure 18-13 Meter Components

Tools For Troubleshooting
When the meter is connected to a circuit, the meter
Wiring Diagrams pointer moves. Pointer movement is called deflection.
Deflection is the measurement of circuit activity.
A wiring diagram is a map of electrical circuits. A suc-
cessful technician uses a diagram to find out where in the Before connecting a meter to a circuit, verify that the
circuit the action should or should not appear. pointer is at zero on the meter scale. See Figure 18-13.

NOTE: For how to read a wiring diagram, see To adjust the pointer to zero for voltage or amperage
“How To Read A Wiring Diagram and Wiring measurements, insert a small screwdriver into the Zero
Key” on page 6. Adjust slot and turn the screw slowly one way or the other
until the pointer is exactly over the zero mark on the
Meters scale.

Meters are the “eyes” that allow a look at the action of an CAUTION: Disconnect any meter from a cir-
electrical circuit. cuit during zero adjustment
• A voltmeter measures voltage.
NOTE: To adjust the pointer on an ohmmeter to
• An ammeter measures current.
zero, hold the meter leads together and rotate
• An ohmmeter measures resistance. the Zero Adjust dial until the pointer remains
over the zero on the meter scale

Page 20 of 44 KM718003 (5/3/00)

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Reading a Voltmeter, Ammeter and Ohmmeter Voltmeter: 0 volts through 1 5 volts.
Ammeter: 0 amperes through 10 amperes.
A successful troubleshooter knows how to read:
Ohmmeter: 0 ohms through infinity (∞).
• A voltmeter for measuring voltage. For meter scale,
see Figure 18-14. When an ohmmeter is not in service and the test
leads of the ohmmeter are not touching anything, the
• An ammeter for measuring current. For meter scale,
pointer usually rests on the infinity (∞) mark. This
see Figure 18-15.
means that there is infinite resistance—an open cir-
• An ohmmeter for measuring resistance. For meter cuit.
scale, see Figure 18-16.
Minor divisions of each scale are represented by the
equal spaces between the major divisions. To find the
value of a minor division, divide the value of the major
division by the number of equal spaces.

Example:
• See voltmeter scale, Figure 18-14.
Position A = 3 volts
B = 7 volts
Figure 18-14 Voltmeter Scale
C = 13 volts
• See ammeter scale, Figure 18-15.
Position A = 1 ampere
B = 1.8 amperes

NOTE: The major divisions have a

value of 1 ampere. Between major divi-
sions are 4 minor divisions. They divide
the scale into 5 equal spaces Each minor divi-
sion has a value of 1 ampere. by 5 spaces = .2
Figure 18-15 Ammeter Scale ampere. Therefore, 1 major division = 1 ampere
and 4 minor divisions @ .2 amperes each = .8
amperes. 1 +.8= 1.8
C = 9 amperes
• See ohmmeter scale, Figure 18-16.
A = 5 ohms
B = 36 ohms
C = 115 ohms
D = 350 ohms
Figure 18-16 Ohmmeter Scale Refer to note that follows:

Numbers mark the major divisions of the scale for each NOTE: For accurate measurements the
meter. When a meter is connected to a circuit, the pointer value of the circuit measured should be
moves over the numbers. This movement is often called designated 2/3 to 4/5 of the full value of
pointer deflection. The number under the pointer is the the meter scale. If pointer deflects to Full Scale,
value of the measurement. Read the scale from left to select a scale with a lower value. If pointer
right. For a voltmeter and ammeter, the extreme right of deflects only slightly, select a scale with a higher
the scale is called Full Scale. value.

(5/3/00) KM718003 Page 21 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
How To Use A Voltmeter The proper method for using an ammeter is to insert it
into the circuit at a fuse or switch. When inserted into the
A DC Voltmeter is connected to a circuit between two circuit, the ammeter completes the circuit by temporarily
points. The voltmeter measures DC voltage between the replacing the fuse or switch. See Figure 18-18.
two points. Voltage exists between two points and does
not flow like current. CAUTION: To prevent meter damage, never
connect an ammeter directly across a volt-
To measure voltage compared to ground: age source, such as a battery.
1. For a 12 volt system, select a 15 volt scale or higher
on the meter’s range selection.
2. Connect the negative (—) terminal of a voltmeter to
the ground (—) location in the circuit.
3. Connect the positive (+) terminal of a voltmeter to the
power (+) location in the circuit.

CAUTION: If the voltmeter is connected with

wrong polarity, the meter pointer may deflect
to the left, damaging the voltmeter.

See Figure 18-17.

Observe the polarity of a DC voltmeter. Connect the neg-

ative terminal of the voltmeter to the negative point of the
circuit. The deflection of the voltmeter pointer shows the
amount of circuit voltage.

Figure 18-18 Ammeter Connections

How To Use An Ohmmeter

An ohmmeter measures the resistance of a circuit or

Figure 18-17 Voltmeter Connections component. Resistance is measured in ohms. Connect
an ohmmeter in parallel with the circuit or component.
How To Use An Ammeter See Figure 18-19.

The shortened word for ampere meter is ammeter. An CAUTION: Before connecting ohmmeter to a
ammeter measures DC current in a circuit. Connect an circuit, disconnect the power source. Failure
ammeter in series with the current flowing from the (+) to to do this could damage the ohmmeter.
(—) through the meter.
NOTE: To verify that the circuit is without volt-
age, connect a voltmeter to the circuit before
connecting the ohmmeter.

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Figure 18-19 Ohmmeter Connections

Resistance is measured by applying a known voltage and

then measuring the current. The voltage for the ohmme-
ter is usually supplied by batteries or a built-in power sup-
ply. With a constant voltage applied to the meter, the
Figure 18-20 Hydrometer
current varies with the resistance measured.
• To determine the proper functioning of the meter, Each cell of a battery contains a solution called electro-
adjust the meter pointer to zero before each test. lyte. Electrolyte is sulfuric acid diluted with water. The
If unable to zero the meter, check the battery. specific gravity of the electrolyte varies with the state of
charge of the cell. A hydrometer measures the specific
• Before connecting the ohmmeter to a circuit, dis- gravity of the electrolyte.
connect the power source.
• When measuring the resistance of a single com- How To Use A Hydrometer
ponent, disconnect the component from the cir-
cuit. WARNING! Batteries contain acid that can
burn and gases that can explode. Ignoring
Hydrometer safety procedures can cause you or others
to be badly hurt.
A hydrometer is a tool for estimating the state of charge WARNING! Do not allow battery fluid to contact
in a battery by measuring the specific gravity of the elec- eyes, skin, fabrics, or painted surfaces. Always
trolyte. wear eye protection. Battery acid that may spill
should be washed off with a solution of warm
A hydrometer consists of: water and baking soda to neutralize the acid. If
• A glass tube containing a weighted and calibrated you accidentally get acid in your eyes or on
float. your skin, immediately rinse with cold water for
several minutes and call a doctor.
• A rubber suction bulb on the upper end of the glass
• Be careful that metal tools (or any metal in contact
tube.
with the positive terminal) do not contact the posi-
• A rubber tube on the lower end of the glass tube. tive battery terminal and any other metal on the
vehicle at the same time. Remove metal jewelry and
NOTE: Some hydrometers are equipped with a avoid leaning over the battery.
thermometer to aid in determining specific grav- • If metal jewelry or other metal comes in contact with
ity. electrical circuits, a short circuit may occur causing
you to be injured, as well as electrical system failure
and damage to the vehicle.

(5/3/00) KM718003 Page 23 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
1. Squeeze the rubber suction bulb on the top end of In a fully-charged battery, the specific gravity of the elec-
the glass tube. trolyte is 1.280 at electrolyte temperature of 80° F. This
specific gravity causes the float to “ride high” As the
2. Insert the rubber tube on the lower end of the glass
charge of the battery decreases, the specific gravity of
tube into the cell of the battery.
the electrolyte decreases, and the float in the hydrometer
3. Release the rubber suction bulb and the electrolyte floats at a lower level in the electrolyte.
will be drawn into the glass tube.
In a discharged battery, the specific gravity of the electro-
4. Read the specific gravity of the electrolyte where the
lyte is 1.150 or less, at 80° F. This specific gravity causes
electrolyte meets the calibrated scale on the float.
the float to “ride low”
NOTE: When reading specific gravity, the float NOTE: Variations in specific gravity from bat-
must be freely suspended in the electrolyte, not tery cell to battery cell should not exceed .025.
touching the walls, top or bottom of the glass
tube. Temperature affects specific gravity readings. Some
hydrometers are equipped with thermometers which tell
Your eye must be approximately on a level with the elec-
how much should be added to or subtracted from the
trolyte in the glass tube. Readings taken at a sharp angle
specific gravity as a result of temperature variations.
may be inaccurate.
As a general rule, do not adjust for temperature differ-
When electrolyte has been gassing freely, allow sediment
ences between 60° F and 100° F. To adjust for large dif-
and gas to escape from the sample before taking a read-
ferences in electrolyte temperature:
ing.
• Add .004 to the specific gravity reading for every 10°
See Figure 18-21. above 80° F.
• Subtract .004 from the specific gravity reading for
every 10° below 80° F.

Example 1:
You have obtained a specific gravity reading of 1.24
with the electrolyte at 1 20° F. Because the tempera-
ture is 40° above the standard 80° F, add .004 x 4 =
.016 to the specific gravity reading. The correct read-
ing is 1.256.

Example 2:
You have obtained a specific gravity reading of 1.25
with the electrolyte at 0° F. Because the temperature
is 80° below standard, subtract .004 x 8 = .032 from
the specific gravity reading. The correct reading is
1.218.

The range of specific gravity of the electrolyte in a cell at

various percentages of full charge is in Figure 18-22.

NOTE: For Centigrade conversion, 80° F = 27°

C For every 5.5° C above 27° C, add .004. For
every 5.5° C below 27° C, subtract .004.

Figure 18-21 Hydrometer With Readings

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Self-Powered Test Light
Specific Gravity and Percentage of Charge
The self-powered test light is a light, battery, and set of
1.280 Sp. Gr. 100% Charged test leads wired in series. The function of a self-powered
test light is to measure continuity like an ohmmeter. How-
1.250 Sp. Gr. 75% Charged
ever, the test light indicates the presence of resistance
1.220 Sp. Gr. 50% Charged but not how much resistance.
1.190 Sp. Gr. 25% Charged CAUTION: Power must be off in circuit dur-
1. 160 Sp. Gr. Very little useful capacity ing test to prevent circuit damage.

1.130 Sp. Gr. Discharged

Figure 18-22 Hydrometer Chart Use for:

• Continuity Check
12 Volt Test Light
• Ground Check
A 12 volt test light is a 12 volt bulb with two test leads.
The function of a test light resembles a voltmeter. How- See Figure 18-24.
ever, the test light indicates the presence of voltage but
not how much voltage.

To connect a test light:

1. Connect 1 test lead to a ground location.
2. Connect 1 test lead to a point where you want a volt-
age check.

NOTE: If a test light is connected across a relay

control circuit, the test light provides enough
grounding to activate the relay without lighting
the test light.

Use for:
• Checking presence of voltage.

NOTE: No voltage indicates presence of an Figure 18-24 Self-Powered Test Light

open in circuit Look for a break in wire or a ter-
minal disconnected.
Tools For Repair
See Figure 18-23. 1. Screwdrivers
2. Wrenches or Nutdrivers
3. Sidecutters
4. Wire Strippers

Figure 18-23 12 Volt Test Light

(5/3/00) KM718003 Page 25 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
A Plan For Finding Electrical Flow Charts For Troubleshooting
Malfunctions These flow charts are for troubleshooting:
1. Circuits and Components
Verify Malfunction
2. Charging System
Before troubleshooting, verify that a malfunction is a mal-
function. Report of a malfunction may be caused by mis- NOTE: Refer to individual Wiring Diagrams for
operation of controls or by an expectation of the system remainder of checks.
performing beyond its design. Verify that:
For instructions in reading a wiring diagram, see “How To
• The controls of the component are operated properly. Read A Wiring Diagram and Wiring Key” on page 6.
• The operator's expectations do not go beyond the
A Wiring diagram will show:
design of the component or system.
• Circuit function.
Troubleshooting Guidelines • Circuit number of all wires in a circuit.
• Destination of wire or purpose of circuit.
The troubleshooting flow charts that follow are organized
around these three guidelines: • Other components on circuit.
• If one component malfunctions in a system with more
NOTE: When troubleshooting, these com-
than one component, begin testing at the malfunc-
ponents are potential problem areas.
tioning component.
• When several components in the same system fail, • Location of:
start testing at the common source of power (circuit
breaker) or common ground. – Terminals

• Test accessible location of circuit before the inacces- – Splices

sible. – Plugs
– Grounds

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Circuits and Components

See next page.

(5/3/00) KM718003 Page 27 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
For Single Component Malfunction • The component is malfunctioning or the component
has an improper ground.
Check voltage at component with voltage test. A voltage
test will tell whether: See Figure 18-25.
• The wiring to the component is in proper operation. NOTE: For how to use a voltmeter, see “Tools For Trou-
bleshooting and Repair” on page 20.

Figure 18-25 Voltage Check

Verify proper voltmeter

ground. See Figure 18-17.

Page 28 of 44 KM718003 (5/3/00)

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Figure 18-26 Check for Low Voltage

Power At Both Sides Of Switch with Switch ON

NOTE: If relay, go to Troubleshooting a Relay on
page 35.

No Yes

1. Check for corrosion at connector(s) between switch

and component.
2. Check for broken wire between switch and compo-
nent.
• Cautiously move the wires while the circuit is in
operation. If the complaint comes and goes,
look for a short circuit or defective connection.
• If wiring diagram shows splice(s) in wire
between switch and component, check splice
area for improper splice.
• When testing with a test light on the power side
of the circuit, progress from the component to
the source of power. See Figure 18-28.

See next page.

(5/3/00) KM718003 Page 29 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Figure 18-27 Check for Low Voltage

Power At Both Sides Of Switch with Switch ON
NOTE: If relay, go to Troubleshooting a Relay on
page 35.

No Yes

1. Check for corrosion at connector(s) between

switch and component.
2. Check for broken wire between switch and compo-
nent.
• Cautiously move the wires while the circuit is
in operation. If the complaint comes and goes,
look for a short circuit or defective connection.
• If wiring diagram shows splice(s) in wire
between switch and component, check splice
area for improper splice.
• When testing with a test light on the power
side of the circuit, progress from the compo-
nent to the source of power. See Figure 18-28.

Page 30 of 44 KM718003 (5/3/00)

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Figure 18-28 Testing With Light

Possible Malfunctions

• Malfunctioning Switch
Yes No Power
NOTE: With switch ON and power to switch
to only one side of switch

Repair or Replace Switch

• Blown fuse or blown circuit breaker

Yes No

Yes
NOTE: If fuse blows repeatedly,
check for overloaded circuit and
visually inspect for grounded cir-
cuit.

See next page.

(5/3/00) KM718003 Page 31 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

• Open wire between switch and circuit breaker.

Continuity check for broken wire

When testing for continuity, use an ohmmeter or self-powered test light. For how to use an
ohmmeter, see page 23; or self-powered test light, see page 25.
1. Verify that all connectors in the circuit are properly connected.
If all connections are properly connected, check for a broken wire.
2. Check wiring harness for cuts or damaged braid that indicates wiring damage.
3. Check wiring diagram for splice(s) in the circuit. If splice(s) are in the circuit, check for
proper connection.
4. Gently wiggle or twist splice area(s) or harness in an attempt to gain momentary electri-
cal contact of broken wire ends. If momentary contact is gained, the malfunction has
been located.

For repair of broken wires, see page 43.

Yes

Repair

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
For Multiple Component Malfunction

Power to Switches
Yes No

Circuit Breaker Blown

Yes No

Replace Circuit Breaker Check for open in wire between switch

NOTE: If fuse blows repeatedly, and circuit breaker. For procedure, see
check for overloaded circuit and Continuity Check for Broken Wire,
visually inspect for grounded cir- page 34.
cuit.

Power At Both Sides Of Switch with Switch ON

Yes No

Repair Switch

NOTE: If Relay, go to Troubleshooting a Relay on page 35.

• Find the central area from where malfunctioning circuits branch out. Check:
• Connectors
• Splice
• Wires

See Figure 18-29.

• Check voltage at each connector, moving from source of power to component. This pro-
cedure will reveal which harness contains improper connections.

See next page. See next page.

(5/3/00) KM718003 Page 33 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Figure 18-29 Check for Low Voltage Connector, Splice or Broken Wire As Logical Problem
Area

Continuity check for broken wire

When testing for continuity, use an ohmmeter or self-powered test light. For how to use an ohmmeter, see
page 23; or self-powered test light, see page 25.
1. Verify that all connectors in the circuit are properly connected.
If all connections are properly connected, check for a broken wire.
2. Check wiring harness for cuts or damaged braid that indicates wiring damage.
3. Check wiring diagram for splice(s) in the circuit. If splice(s) are in the circuit, check for proper connection.
4. Gently wiggle or twist splice area(s) or harness in an attempt to gain momentary electrical contact of bro-
ken wire ends. If momentary contact is gained, the malfunction has been located.

For repair of broken wires, see page 43.

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Troubleshooting A Relay

Figure 18-30 Typical Relay Circuit

1. Remove relay from socket.
2. Check voltage at relay with a voltage test.
(See Figure 18-31).

Figure 18-31 Check Voltage to Relay

(5/3/00) KM718003 Page 35 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Power on Power Side of Relay (Switch Portion)

No Yes

Blown Fuse or Circuit Breaker

Yes No

Replace fuse

Open in Wire Between Switch and Circuit Breaker.

Continuity Check for Broken Wire

When testing for continuity, use an ohmmeter or self-pow-

ered test light. For how to use an ohmmeter, see page 23;
or self-powered test light, see page 25.
1. Verify that all connectors in the circuit are properly con-
nected.
If all connections are properly connected, check for a
broken wire.

2. Check wiring harness for cuts or damaged braid that

indicates wiring damage.
3. Check wiring diagram for splice(s) in the circuit. If
splice(s) are in the circuit, check for proper connection.
4. Gently wiggle or twist splice area(s) or harness in an
attempt to gain momentary electrical contact of broken
wire ends. If momentary contact is gained, the malfunc-
tion has been located.

For repair of broken wires, see page 43.

Yes

Place jumper wire across switch

protion of relay. See Figure 18-32,
Repair
Jumper Across Switch Portion of
Relay

See next page.

Page 36 of 44 KM718003 (5/3/00)

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Figure 18-32 Jumper Across Switch Portion of Relay

With Jumper Across Switch Portion of Relay Socket.

Voltage At Component No Voltage At Component
NOTE: Problem with relay or relay NOTE: Problem between relay or component.
control circuit.

1. Check for corrosion at connector(s) between

switch and component.
2. Check for broken wire between switch and com-
ponent.
• Cautiously move the wires while the circuit
is in operation. If the complaint comes and
goes, look for a short circuit or defective
connection.
• If wiring diagram shows splice(s) in wire
between switch and component, check
splice area for improper splice.
• When testing with a test light on the power
side of the circuit, progress from the compo-
Check Voltage Across Relay Coil Terminals. nent to the source of power. See Figure
See Figure 18-33, Check Voltage Across Relay 18-28.
Coil Terminals.

See next page.

(5/3/00) KM718003 Page 37 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Figure 18-33 Check Voltage Across Relay Coil Terminals

Voltage Across Relay Coil Terminals

Correct Voltage No Voltage
NOTE: Voltage with
switch ON, no voltage
with switch OFF.

Malfunctioning Relay

Replace Relay

Check for Power At One of the Coil Terminals

Power No Power
NOTE: Coil of some relays is actuated via
a fuse or circuit breaker different from the
one for component operated by relay.

Blown Fuse or Blown Circuit Breaker

No Yes

Open Wire Between Relay Replace

and Circuit Breaker

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Continuity Check For Broken Wire

When testing for continuity, use an ohmmeter or self-powered test light. For how to use an
ohmmeter, see page 23; or self-powered test light, see page 25.
1. Verify that all connectors in the circuit are properly connected.
If all connections are properly connected, check for a broken wire.

2. Check wiring harness for cuts or damaged braid that indicates wiring damage.
3. Check wiring diagram for splice(s) in the circuit. If splice(s) are in the circuit, check for
proper connection.
4. Gently wiggle or twist splice area(s) or harness in an attempt to gain momentary electri-
cal contact of broken wire ends. If momentary contact is gained, the malfunction has
been located.

For repair of broken wires, see page 43.

Yes

Repair

Check for Ground At Other Coil Terminal (Switched Side)

When testing for continuity, use an ohmmeter or self-powered test light. For how to use an ohmmeter,
see page 23; or self-powered test light, see page 25.

No Ground Regardless Ground Regardless of

of Switch Position Switch Position

Ground the wire At Switch Controlling the

Relay. See Figure 18-34, Jumper to
Bypass Switch.

See next page. See next page.

(5/3/00) KM718003 Page 39 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Figure 18-34 Jumper to Bypass Switch

Ground at Relay Terminal No Ground at Relay Terminal

Check Switch Open Wire Between Switch and Relay

NOTE: Verify proper switch
ground. Disconnect Wire at Switch
See Figure 18-35, Disconnect Wire at Switch.

Figure 18-35 Disconnect Wire at Switch

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
Charging System

Low Battery Charge

(5/3/00) KM718003 Page 41 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18

Excessive circuit resistance. Check battery.

Check for corroded connectors in

charging circuit.

Check circuit breakers in charging circuit.

NOTE: A malfunctioning circuit breaker may
interrupt charge current to batteries.

Malfunctioning Battery
Check battery in accordance with manufacturer’s specifications. A battery will remain in a discharge condition
under normal operating conditions if it has:
• Exhausted service life.
• An open circuit at a terminal post.
• An open circuit in one cell.
• Shorted battery cells

Check each cell with hydrometer. One cell will have a low reading if cell is shorted.

NOTE: For how to use a hydrometer, see How To Use A Hydrometer on page 23.

Overcharged Battery: For rapid loss of water from battery cells, check:

Output of alternator.
OK Too High

Repair Regulator/Alternator

Check

Check Battery for shorted cell.

Check with hydrometer. One cell will have a low reading if cell is shorted.
NOTE: For how to use a hydrometer, see How To Use A Hydrometer on page 23.

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 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
How To Repair Electrical Malfunctions

Components
• Circuit Breaker
• Fuse
• Gauge or Sending Unit
• Motor
• Power Distribution Box
– Printed Circuit Board
• Relay
Figure 18-36 Wire Strippers
• Series/Parallel Switch
5. Solder splice. See Figure 18-37
• Solenoid
• Switch

The quickest method of correcting a malfunction of these

components is to replace the component. If the compo-
nent does not operate properly, refer to Section 5, A Plan
For Finding Electrical Malfunctions.

Broken Wire
For how to find a broken wire or splice, see Continuity
Check for Broken Wire, page 26.

How To Repair A Broken Wire

1. With wire strippers, strip 1/2 inch of insulation from
broken end of each wire.
2. Slide plastic heat shrink tube over wire end 6-8 Figure 18-37 Soldering of Splice
inches away from area of splice.
6. Position plastic heat shrink tube over splice. See Fig-
3. Position metal splice around each end of broken ure 18-38.
wire.
NOTE: Splice may also be protected with
NOTE: Metal splice must cover all of electrical tape.
exposed wire.
7. Apply heat to shrink tube. See Figure 18-39.
4. Crimp metal splice. See Figure 18-36

(5/3/00) KM718003 Page 43 of 44

 MEDIUM DUTY MAINTENANCE MANUAL
Electrical System Troubleshooting - T300 18
How To Replace An Electrical Connector.

NOTE: Each terminal of the new connector

must be connected with the same wire to which
the terminal of the old connector was con-
nected.
1. Before removing connector, identify each terminal by
affixing a tag with a letter to the wire of the terminal.
See Figure 18-40.

Figure 18-38 Position of Heat Shrink

Figure 18-40 Replacing a Connector

2. Identify each terminal of the new plug by affixing a
tag with a letter to the wire of the terminal.

NOTE: Verify that terminals A through G of new

connectors are like terminals A through G of
connector to be replaced.
3. With appropriate tool, cut wire A of connector to be
replaced.
4. Splice wire A of connector to be replaced with wire A
Figure 18-39 Heating of Heat Shrink of new connector.

Replacing An Electrical Connector NOTE: Follow procedure in this section for How
To Repair A Broken Wire.
Many types of connectors are installed in an electrical
system. The 8-way connector is a typical connector. The Repeat steps 3 and 4 for each wire of connector.
following procedure for replacement applies to most con-
nectors.

Page 44 of 44 KM718003 (5/3/00)