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Headlamp Wiring
The headlamp wiring is protected by a circuit
breaker in the light switch. An electrical overload
will cause the lights to go on and off, or in
some cases to remain off. If this happens, have
your headlamp wiring checked right away.
Windshield Wiper Fuses
The windshield wiper motor is protected by a
circuit breaker inside the motor and a circuit
breaker or fuse in the fuse block. If the motor
overheats, the wipers will stop until the motor
cools. If the overload is caused by an electrical
problem, be sure to get it fixed.
Fusible Links
A fusible link is a short piece of wire several gauge
sizes smaller than the circuit it protects. It will melt
in an overload situation, opening the circuit.
Your starter and other circuits have these fusible
links. The size is printed on the insulation. If the
insulation is burned beyond recognition, consult
your dealer for the proper size. Replace a fusiblelink with one of the same size and insulation type.
Fusible link insulation is a special purpose
high-temperature material.
Some examples of circuits with fusible links are
the hydraulic brake booster motor feed circuit, the
generator output circuit, and the intake heater
feed circuit in vehicles with a diesel engine.
Power Windows and Other
Power Options
Circuit breakers in the fuse panel protect the power
windows and other power accessories. When the
current load is too heavy, the circuit breaker opens.
This protects the circuit until the current load returns
to normal or the problem is fixed.
Fuses and Circuit Breakers
The wiring circuits in your vehicle are protected
from short circuits by a combination of fuses, circuit
breakers, maxi-fuses and fusible links. This greatly
reduces the chance of a fire caused by an electrical
problem. There may be a fuse taped to the wiring
harness near the hydraulic brake booster.
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Instrument Panel Fuse Block
There are two instrument panel fuse blocks located behind the instrument panel on the passenger’s side of
the vehicle. Be sure to replace fuses with fuses of the same rating. Do not use fuses of higher amperage
than those indicated on the fuse block.
Fuse Usage
1 Stoplamps
2 Center High-Mounted Stoplamp
3 Parking LampsFuse Usage
4 Powertrain Control Module
5 Auxiliary Wiring
6 Heater/Air Conditioning
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Fuse Usage
7 Hazard Warning Flashers
8 Power Post
9 Courtesy Lamps
10 Warning Lights, Gages and Indicators
11 Starter
12 Rear Axle/Four-Wheel-Drive
13Trailer Turn Signals/Hazard Warning
Flashers
14 Radio/Chime
15 Daytime Running Lamps
16 Airbag System
17 Exterior/Interior Lamps
18 Parking Brake
19 Accessory Power
20 Ignition 4
21 Sidemarker Lamps
22 Turn Signal/Backup Lamps
23 TransmissionFuse Usage
24 Hydraulics/Air Brake
A Spare
B Spare
Fuse Usage
Blank Not Used
BRK Brake Warning Lamp
RT PRK Passenger’s Side Parking Lamps
Blank Not Used
Blank Not Used
LT PARK Driver’s Side Parking Lamps
RT REAR
TRN/STOPPassenger’s Side Rear Turn
Signal/Stoplamp
LT REAR
TRN/STOPDriver’s Side Rear Turn
Signal/Stoplamp
RADIO Radio
Blank Not Used
Blank Not Used
PWR WNDW Power Windows
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Relay Usage
ECU/PTO*Engine Control Unit/Power Take-Off
*Diesel 7.8 DURAMAX
®
BRK LAMPC4/C5 Brake Lamps,
C6/C7/C8 Tractor/Trailer Wiring
DRL Daytime Running Lamps
IGN-4 Ignition
CHMSL Center High Mounted Stoplamp
MRK LTS Sidemarker and Clearance Lamps
HTD/MIRR Heated Mirrors
HTR Diesel Heated Fuel
RT TRN TRLR Passenger’s Side Trailer Turn Signal
Blank Not Used
LT TRN TRLR Driver’s Side Trailer Turn Signal
Blank Not Used
Blank Not Used
Blank Not Used
Underhood Fuse Block
When a circuit goes out, the problem could be in
either the primary or secondary underhood
fuse blocks. These blocks use blade-type fuses.
Both underhood fuse blocks are located in
the engine compartment, on the passenger’s side
of the vehicle.
To access the fuse blocks, gently squeeze both
sides of the cover to unlatch the tabs at the
top. Then, unsnap both attachments at the bottom
and remove the cover.
Be sure to replace fuses with fuses of the same
rating. Do not use fuses of higher amperage
than those indicated on the fuse block.
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Fuse Usage
RR DEFOG Rear Defogger
ENG 1 Engine 1
ENG 3 Engine 3
PCM-B Powertrain Control Module
Fuse Usage
BLANK Not Used
ENG 4 Engine 4
ENG 2 Engine 2
HTD FUEL Heated Fuel
BLANK Not Used
BLANK Not Used
02A Emissions
A/C COMP Air Conditioning Compressor
ABS 1 Anti-lock Brake System 1
ABS 2 Anti-lock Brake System 2
ABS 3 Anti-lock Brake System 3
ENGINE Engine
E/A PUMP Electronic/Automatic Pump
HORN Horn
NOTE 2L18 Fuel, LG4 Powertrain Control
Valve, LG5 Electronic Control
Module Primary Underhood Fuse Block
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Fuse Usage
NOTE 3L18 Fuel, LG4 Powertrain Control
Valve, LG5 Electronic Control
Module
STUD A Spare
STUD B Spare
Relay Usage
NOTE 1LLY/L18 Fuel Pump Relay, LG4/LG5
Heated Fuel Relay
IGN B Ignition Relay
STARTER Starter Relay
HORN Horn Relay
IGN A Ignition Relay
PTO/ECU*Power Take-Off/Engine Control Unit
(*Diesel 7.8L LG4)
REVERSE Reverse Relay
NEUTRAL
STARTNeutral Start (LG4 Allison Automatic
Transmission Series 3000/3500)
Fuse Usage
IGN 1 Ignition 1
IGN 4 Ignition 4
IGN 3 Ignition 3
BATT/HAZ Battery/Hazard Warning Flashers
HEADLAMP Headlamps
LIGHTING Interior/Exterior Lamps
HVAC Climate Control System
NOTEC4/C5 Electric Brake,
C6/C7/C8 Brake Lamps Secondary Underhood
Fuse Block
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E
Electrical System
Add-On Equipment................................... 340
Fuses and Circuit Breakers...................... 341
Fusible Links............................................ 341
Headlamp Wiring..................................... 341
Instrument Panel Fuse Block................... 342
Power Windows and Other Power
Options................................................. 341
Underhood Fuse Block............................. 344
Windshield Wiper Fuses........................... 341
Engine
Air Cleaner/Filter...................................... 280
Alarm and Automatic Shutdown................ 104
Battery..................................................... 304
Change Engine Oil Light.......................... 176
Check and Service Engine Soon Light..... 174
Checks Before Operating......................... 109
Coolant...........................................284, 287
Coolant Heater......................................... 111
Coolant Temperature Gage...................... 173
Diesel Engine Exhaust Brake................... 112
Drive Belt Routing.................................... 355
Exhaust................................................... 131
Exhaust Restrictor.................................... 108
Fan Breakage.......................................... 250Engine (cont.)
Fan Noise................................................ 294
High Idle System..................................... 106
Oil ...................................................268, 272
Oil Life System.......................276, 278, 279
Overheating............................................. 288
Overspeed Warning Light......................... 177
Reduced Power Light............................... 179
Shutdown Warning Light.......................... 177
Speed Limiter.......................................... 164
Starter Over-Crank Protection.................... 97
Starting Your Diesel................................. 100
Starting Your Gasoline............................... 97
Entry Lighting.............................................. 154
Event Data Recorders (EDR)...................... 409
Exhaust Brake Indicator Light...................... 178
Exhaust Restrictor....................................... 108
Extender, Safety Belt..................................... 41
Exterior Lamps............................................ 150
F
Filter
Engine Air Cleaner................................... 280
Filter Minder Gage...................................... 182
Finish Damage............................................ 338
Fixed Mast Antenna.................................... 204
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Flashers, Hazard Warning........................... 142
Flat Tire...................................................... 330
Fluid
Automatic Transmission............................ 282
Manual Transmission................................ 283
Power Steering........................................ 295
Windshield Washer.................................. 296
Four-Wheel Drive...............................119, 312
Front Axle................................................... 313
Front Wheel Bearings with Oil-Filled Hubs ... 319
Fuel............................................................ 251
Additives.................................................. 252
Diesel Engine Fuel................................... 253
Filling a Portable Fuel Container.............. 266
Filling Your Tank...................................... 264
Filter........................................................ 317
Filter Replacement................................... 263
Fuels in Foreign Countries....................... 264
Gage....................................................... 181
Gasoline Octane...................................... 251
Gasoline Specifications............................ 251
Primary Filter and Water Separator.......... 317
Running Out of Fuel................................ 262
Secondary Filter and Water Separator/
Heater.................................................. 318
Very Cold Weather Operation................... 256
Water in Fuel........................................... 256Fuel (cont.)
Water in Warning Light............................ 182
What Fuel to Use.................................... 253
Fuses
Fuses and Circuit Breakers...................... 341
Instrument Panel Fuse Block................... 342
Underhood Fuse Block............................. 344
Windshield Wiper..................................... 341
G
Gage
Air Pressure............................................. 183
Check Gages Warning Light..................... 180
Engine Coolant Temperature.................... 173
Filter Minder............................................ 182
Fuel......................................................... 181
Hourmeter................................................ 183
Oil Pressure............................................. 175
Speedometer........................................... 163
Tachometer.............................................. 163
Transmission Temperature........................ 178
Voltmeter Gage........................................ 168
Gasoline
Octane..................................................... 251
Specifications........................................... 251
Gasoline Engine, Starting.............................. 97
GM Mobility Reimbursement Program.......... 407
422