Instrument Panel Fuse Block
There are two instrument panel fuse blocks located behind the instrument panel on the passenger’s side of the vehicle.
| Circuit Breaker | Usage |
| 1 | Stoplamps |
| 2 | Not Used |
| 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 | Starter |
| 12 | Rear Axle/Four-Wheel-Drive |
| 13 | Trailer 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 | Transmission |
| 24 | Hydraulics/Air Brake |
| A | Spare |
| B | Spare |
| Fuse | Usage |
| Blanj | Not Used |
| RT PRK | Passenger’s Side Parking Lamps |
| Blank | Not Used |
| Blank | Not Used |
| LT PARK | Driver’s Side Parking Lamps |
| RT REAR TRN/STOP | Passenger’s Side Rear Turn Signal/Stoplamp |
| LT REAR TRN/STOP | Driver’s Side Rear Turn Signal/Stoplamp |
| RADIO | Radio |
| Blank | Not Used |
| Blank | Not Used |
| PWR WNDW | Power Windows |
| Relay | Usage |
| ECU/PTO* | Engine Control Unit/Power Take-Off *Diesel 7.8 DURAMAX® |
| BRK LAMP | C4/C5 Brake Lamps, C6/C7/C8 Tractor/Trailer Wiring |
| DRL | Daytime Running Lamps |
| IGN-4 | Ignition |
| CHMSL | Center High Mounted Stop Lamp |
| 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
Fuse blocks are located in the engine compartment, on the passenger’s side of the vehicle.
Primary Underhood Fuse Block
| Fuse | Usage |
| RR DEFOG | Rear Defog |
| ENG 1 | Engine 1 |
| ENG 3 | Engine 3 (L18/LF6/LF8) |
| PCM-B | Powertrain Control Module |
| TCM | Transmissions (LF8) |
| ENG 4 | Engine 4 (LMM/LF6/LF8) |
| ENG 2 | Engine 2 (L18/LMM) |
| HTD FUEL | Heated Fuel (LMM) |
| BLANK | Not Used |
| BLANK | Not Used |
| NOTE 3 | Fan Relay (LMM), Emissions (L18) |
| 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 2 | Fuel (L18/LMM), Electronic Control Module (LF6) |
| NOTE 3 | Electronic Control Module (LF6) |
| STUD A | Spare |
| STUD B | Spare |
| Relay | Usage |
| NOTE 1 | LMM/L18 Fuel Pump Relay |
| IGN B RELAY | Ignition Relay |
| STARTER RELAY | Starter Relay |
| HORN RELAY | Horn Relay |
| IGN A RELAY | Ignition Relay |
| PTO/ECU* RELAY | Power Take-Off/Engine Control Unit (*Diesel 7.8L LF8) |
| REVERSE RELAY | Reverse Relay |
| FAN RELAY | Fan Relay (LMM) |
Secondary Underhood 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 | Climate 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.