GMC T-Series mk3 (2003 – 2006) – fuse box diagram
Year of production: 2003, 2004, 2005, 2006
Instrument Panel Circuit Breaker and Relay Blocks
These circuit breaker and relay blocks are located on top of the instrument panel on the passenger’s side of the cab.
| Number | Circuits Protected |
| 1 | Ignition Switch |
| 2 | Cigarette Lighter |
| 3 | ECM Ignition 1 |
| 4 | Truck Body Controller |
| 5 | ALDL Connector |
| 6 | Warning Lamp, Ignition Relay, Blower Motor, Motor Relay, Auxiliary Relay, Power Window Relay, INT Relay |
| 7 | Room Lamp, Horn, Electric Parking Brake, Radio Back Up, Rear Body Dome Lamp |
| 8 | Power Window |
| 9 | Exhaust Brake Back Up, Air Suspension Dump, Differential Lock, Air Dryer, Moisture Ejection Heater, Electric Air Compressor, Power Take Off |
| 10 | ECM Ignition Power |
| 11 | Trailer Turn (LH) Lamp |
| 12 | Auxiliary (Ignition ON) |
| 13 | Auxiliary (Battery Direct) |
| 14 | Headlamp (LH) |
| 15 | Headlamp (RH) |
| 16 | Headlamp |
| 17 | Heated Fuel |
| 18 | Meter Truck Body Controller |
| 19 | ID Lamp, Marker Lamp, Tail Lamp, Lighted Mirror, Illumination Lamp |
| 20 | Cool Condenser Fan Motor, Cooler Compressor |
| 21 | Wiper Motor, Washer Motor |
| 22 | Heated Mirror, Two-Speed Axle Relay |
| 23 | Empty |
| 24 | Blower Motor, Air Conditioner Relay |
| 25 | Trailer Turn (RH) Lamp, Flasher Unit |
| 26 | Power Post (Consent) |
Maxi-Fuse Block
Maxi-Fuse block is located outside of the cab at the rear, on the driver’s side.
| Name | Circuits/Circuit Breakers Protected |
| ST/TURN/HAZ | Stoplamp, Turn Signals/Hazard Warning Flashers |
| IGN SW3 | Air Conditioner, Axle, Chassis |
| INT/EXT LIGHTS | Parking Lamps, Dome Lamp, Instrument Panel Lights |
| HEAD LAMP | Headlamps, Daytime Running Lamps |
| AUX WRG | Auxiliary, Parking Brake |
| IGN SW1 | Ignition Switch, Washer/Wiper, Crank, Radio |
| HYD PUMP | Hydraulic Brake, Brake Pump Motor |
| ABS | Anti-Lock Brake System Module |
| ELECT TRANS | Ignition Relay |
| PARK BRAKE | Parking Brake Motor |
| BLOWER HORN | Blower, Horn, Cigarette Lighter, Auxiliary |
| TRAILER ABS | Trailer Anti-Lock Brake System, Trailer Stoplamps |
| PWR WDO/LOCKS | Power Windows, Power Door Locks |
Relay Blocks
There are three relay blocks in your vehicle.
| Relay | Relay block |
| A | Relay Block A |
| B | Relay Block B |
| C | Relay Block C |
Relay Block A
| Relay Block A | Usage |
| 1 | Power Window |
| 2 | Back Lamp (Reverse) |
| 3 | High Beam |
| 4 | Lighting |
| 5 | Lighting (Low, High) |
| 6 | Trailer Turn Signal (Left Headlamp) |
| 7 | Tail Lamp |
| 8 | Marker Lamp |
| 9 | Trailer Turn Signal (Right Headlamp) |
Relay Block B
| Relay Block B | Usage |
| 1 | Air Conditioning Condenser |
| 2 | Air Conditioning Compressor |
| 3 | Heater Fan |
| 4 | Ignition Accessory |
| 5 | Ignition 1 |
| 6 | Ignition 2 |
| 7 | Auxiliary |
| 8 | Horn |
| 9 | Ignition 3 |
| 10 | Dome Lamp |
| 11 | Exhaust Brake |
| 12 | Power Take Off Control |
Relay Block C
| Relay Block C | Usage |
| 1 | Parking Brake |
| 2 | Daytime Running Lamps On |
| 3 | Daytime Running Lamp Off |
| 4 | Parking Lamps/Daytime Running Lamps |
| 5 | Neutral |
| 6 | Stop Lamp |
WARNING: Terminal and harness assignments for individual connectors will vary depending on vehicle equipment level, model, and market.
