TL;DR
- Main fuse box: the front power distribution box in the engine compartment holds 46 fuses and 15 relays (Bentley).
- More fuses and relays: the auxiliary relay panel under the left side of the dashboard, the left and right splice panels, and on later cars a fuse in the right side of the luggage compartment.
- Fuse assignments changed every model year and depend on equipment and market. Bentley prints a separate table for each year from 1992 to 1998. The chart in your fuse box lid, or the wiring diagrams for your car, is the authority.
- Always replace a fuse with the same rating. A bigger fuse can cause circuit damage or a fire.
Where everything is
| Location | What’s there (Bentley) |
|---|---|
| Front power distribution box, engine compartment | Fuses 1–46 and relay positions 1–15 |
| Auxiliary relay panel, under the left side of the dashboard | Comfort relay (where fitted), crash control module, park ventilation relay; on cars from January 1995 the EWS II transmitter/receiver module; fuse 48 |
| Left splice panel | Fuses 47 and 50 (later cars) |
| Right side of the luggage compartment | Fuse 49 (later cars) |
Relays in the front power distribution box (Bentley)
| Position | Relay |
|---|---|
| 1 | Fuel pump relay |
| 2 | System (main) relay |
| 3 | Oxygen sensor heater relay |
| 4 | Horn relay |
| 5 | Taillight / foglight relay |
| 6 | Low beam relay |
| 7 | High beam relay |
| 8 | Emergency flasher relay |
| 9 | Heater / A/C blower relay |
| 10 | Rear defogger relay |
| 11 | ABS system relay |
| 12 | ABS pump relay |
| 13 | High-speed radiator fan relay |
| 14 | A/C compressor relay |
| 15 | Low-speed radiator fan relay |
Relay positions can vary from car to car. Bentley’s tip: verify a relay by comparing the wire colours at its socket with the wiring diagram.
The fuel pump relay and the “priming hum”
On the M50’s Bosch DME M3.1 and M3.3.1, Bentley’s pin tables state that the DME switches the fuel pump relay only while the engine is cranking or running: the crankshaft position signal must be present. So no pump noise with the ignition just switched on is normal on these cars, not a fault. To test the pump on its own, Bentley bridges the relay socket’s terminals 30 and 87 with a fused jumper. See the fuel system guide.
1994 fuse positions (Bentley Table d, front power distribution box)
Main circuit per fuse; many fuses feed several circuits. This is Bentley’s US-market 1994 table: European cars and other years differ, so check your own car’s chart.
| Fuse | Rating | Main circuit(s) |
|---|---|---|
| 1 | 30A | Power sunroof |
| 2 | 15A | Not used |
| 3 | 30A | Headlight washer |
| 4 | 15A | Heated seats |
| 5 | 30A | Power seats |
| 6 | 20A | Rear window defogger / blower |
| 7 | — | Central body electronics (convertible), central locking, convertible roof |
| 8 | 15A | Horn |
| 9 | 20A | Sound system |
| 10 | 30A | ABS / traction control |
| 11, 12 | 7.5A | Headlights / foglights, on-board computer |
| 13 | 5A | Not used |
| 14 | 30A | Front power windows |
| 15 | 15A | Headlights / foglights |
| 16 | 5A | Engine control module; heating and A/C |
| 17 | 10A | Not used |
| 18 | 15A | Fuel pump |
| 19 | 30A | Rear power windows |
| 20 | 30A | Blower motor |
| 21 | 5A | ABS / traction control |
| 22 | 5A | Instrument illumination, park/taillights |
| 23 | 5A | Headlights/foglights, heated seats, instrument cluster, turn signals and others |
| 24 | 10A | Power mirrors |
| 25 | 5A | Headlights/foglights, instrument illumination |
| 26 | 10A | Back-up lights; automatic transmission control |
| 27 | 5A | Instrument cluster, on-board computer |
| 28 | 5A | Cruise control, engine control module, starting system |
| 29, 30 | 7.5A | Headlights / foglights |
| 31 | 5A | Clock, heating and A/C, instrument cluster |
| 32 | 30A | Cigar lighter / ashtray lights |
| 33 | 10A | Central body electronics, interior lights, licence plate and luggage compartment lights, park/taillights |
| 34 | 15A | Crash control module, turn signals / hazard lights |
| 35 | 25A | Central locking, convertible roof, roll-over protection |
| 36 | 30A | Wiper / washer |
| 37 | 10A | Engine compartment light, instrument illumination, lights and others |
| 38 | 30A | ABS / traction control |
| 39 | 7.5A | Heating and A/C |
| 40 | 30A | Power seats |
| 41 | 30A | Heating and A/C, radiator auxiliary fan |
| 42 | 7.5A | Airbag (SRS), roll-over protection |
| 43 | 5A | Anti-theft system, airbag, central body electronics |
| 44 | 15A | Glove compartment light and others |
| 46 | 15A | ABS, brake lights, cruise control, instrument cluster and others |
Finding a blown fuse
- List what stopped working. Several unrelated items at once suggest a shared fuse, or a bad ground (see the ground guide).
- Find the fuse for that circuit on your lid chart or in the wiring diagrams.
- Ignition off before pulling fuses or relays. For any other electrical work, also disconnect the battery negative cable (in the boot), observing your car’s battery-disconnection cautions. On cars with airbags, follow the airbag precautions first.
- Check it properly: a hairline crack can hide in the element. Better than looking: measure voltage on both sides of the fuse with the circuit switched on.
- Find the cause. A new fuse that blows at once means a hard short; one that blows later points to an intermittent short or an overloaded circuit.
Never fit a fuse of a higher rating to stop one from blowing.
Blade fuse colours
| Colour | Rating |
|---|---|
| Tan | 5A |
| Brown | 7.5A |
| Red | 10A |
| Blue | 15A |
| Yellow | 20A |
| Clear / natural | 25A |
| Green | 30A |
After an M43 → M50 swap
- The M50 engine harness plugs into the same chassis connector, and the engine-management fuses and relays (system relay, fuel pump relay, oxygen sensor heater relay) are already in the front box.
- No fuel pump priming hum is normal on an M3.1/M3.3.1 car; the pump runs while cranking.
- The six-cylinder auxiliary fan relies on its relays and fuse in the front box and on the radiator’s temperature switch. Check the fan works after the swap.
