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GMC C-Series mk3 (Third Generation; 2003 - 2009) Fuse Box Diagram

avatar Jonathan Yarden Mar 25, 2021 · 5 min. read

In this article you will find a description of fuses and relays GMC, with photos of block diagrams and their locations. Highlighted the cigarette lighter fuse (as the most popular thing people look for).
Get tips on blown fuses, replacing a fuse, and more.

Year of production: 2003, 2004, 2005, 2006, 2007, 2008, 2009

Instrument Panel

There are two instrument panel fuse blocks located behind the instrument panel on the passenger’s side of the vehicle.

Fuse block 1

GMC C-Series mk3 - fuse box - instrument panel (fuse block 1)

Fuse Circuits protected
RH PARK LP Right-hand Parking Lamps
LH PARK LP Left-hand Parking Lamps
PWR WINDOW Power Windows
BRAKE ISO Brake Warning Lamp
SPARE Spare Fuse
L-RR TRUCK Left Rear Trailer Wiring
SPARE Spare Fuse
SPARE Spare Fuse
SPARE Spare Fuse
R-RR TRUCK Right Rear Trailer Wiring
SPARE Spare Fuse

Relay Circuits protected
BRAKE LAMP C4/C5 Brake Lamps, C6/C7/C8 Tractor/Trailer Wiring
IGN 4 Ignition
MARKER LP Sidemarker and Clearance Lamps
HTD FUEL LB7/LG4 Heated Fuel
AIR HTR LG4 Air Heater
ECU MAINTAIN LG4 Electronic Control Unit
DRL Daytime Running Lamps
CHMSL ISO Center High Mounted Stop Lamp
HTD MIRR Heated Mirrors
R-TRN TLR Right Trailer Turn Signal
L-TRN TLR Left Trailer Turn Signal
SPARE Spare Relay
SPARE Spare Relay
SPARE Spare Relay

Fuse block 2

GMC C-Series mk3 - fuse box - instrument panel (fuse block 2)

Circuit Breaker Usage
1 Stoplamps
2 Center High Mounted Stop Lamp
3 Parking Lamps
4 Powertrain Control Module
5 Auxiliary Wiring
6 Heater/Air Conditioning
7 Hazard Warning Flashers
8 Power Post
9 Courtesy Lamps
10 Warning Lights, Gages and Indicators
11 Crank
12 Rear Axle
13 Trailer Turn Signals/Hazard Warning Flashers
14 Radio/Chime
15 Daytime Running Lamps
16 Air Bag System
17 Exterior/Interior Lamps
18 Parking Brake
19 Accessory Power
20 Ignition
21 Sidemarker Lamps
22 Turn Signal/Backup Lamps
23 Transmission
24 Chassis
A Spare
B Spare


Underhood Fuse Block

There are two underhood fuse blocks located in the engine compartment, on the
passenger’s side of the vehicle.

Primary Underhood fuse block

GMC C-Series mk3 - fuse box - engine compartment (primary fuse block)

Relay Usage
NOTE 1 LG4 Powertrain Control Valve, L18/LB7 Fuel Pump, LG5 Heated Fuel
IGN B Ignition
IGN A Ignition
PTO Power Take-Off

Fuse Usage
RR DEFOG Rear Defog
ENG 1 Engine 1
ENG 3 Engine 3
PCM-B Powertrain Control Module
ENG 4 Engine 4
ENG 2 Engine 2
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
E/A PUMP Electronic/Automatic Pump
NOTE 2 L18/LB7 Fuel, LG4 Powertrain Control Valve, LG5 Electronic Control Module
STUD A Spare
STUD B Spare

Secondary Underhood Fuse Block

GMC C-Series mk3 - fuse box - engine compartment (secondary fuse block)

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 Comfort Control System
NOTE C4/C5 Electric Brake, C6/C7/C8 Brake Lamps

WARNING: Terminal and harness assignments for individual connectors will vary depending on vehicle equipment level, model, and market.

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