| 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 |
GMC Topkick 2008 Instrument Panel Fuse Panel / Board – Fuse Symbol Map
| No. | Fuse | Usage |
|---|---|---|
| 1 | Blank | Not Used |
| 2 | RT PRK | Passenger’s Side Parking Lamps |
| 3 | Blank | Not Used |
| 4 | Blank | Not Used |
| 5 | LT PARK | Driver’s Side Parking Lamps |
| 6 | RT REAR TRN/STOP | Passenger’s Side Rear Turn Signal/Stoplamp |
| 7 | LT REAR TRN/STOP | Driver’s Side Rear Turn Signal/Stoplamp |
| 8 | RADIO | Radio |
| 9 | Blank | Not Used |
| 10 | Blank | Not Used |
| 11 | PWR WNDW | Power Windows |
| No. | Relay | Usage |
|---|---|---|
| 1 | ECU/PTO* | Engine Control Unit/Power Take-Off *Diesel 7.8 DURAMAX® |
| 2 | BRK LAMP | C4/C5 Brake Lamps, C6/C7/C8 Tractor/Trailer Wiring DRL Daytime Running Lamps |
| 3 | IGN-4 | Ignition |
| 4 | CHMSL | Center High Mounted Stop Lamp |
| 5 | MRK LTS | Sidemarker and Clearance Lamps |
| 6 | HTD/MIRR | Heated Mirrors |
| 7 | HTR | Diesel Heated Fuel |
| 8 | RT TRN TRLR | Passenger’s Side Trailer Turn Signal |
| 9 | Blank | Not Used |
| 10 | LT TRN TRLR | Driver’s Side Trailer Turn Signal |
| 11 | Blank | Not Used |
| 12 | Blank | Not Used |
| 13 | Blank | Not Used |
