Fuses and relays
Fuses and relays refers to the fuse block, fuses, circuit breakers, fusible links, and relay-controlled circuits used in the Pontiac Fiero electrical system.
On the Fiero, many electrical problems can be traced to a blown fuse, poor fuse-block contact, a failed circuit breaker, a bad ground, damaged wiring, or a failed relay in a specific circuit.
Fuse access location
The main fuse block is located under the left side of the instrument panel, on the driver's side.
Access to the fuses is through a fuse-block access door under the left side of the dash. The access door is released by pushing inward on the two release tabs near the center and swinging the door down toward the seat.
This location makes the fuse block accessible from the driver's footwell area.
Fuse block layout
The Fiero fuse block contains standard blade fuses and circuit breakers.
The fuse block includes circuits for engine control, fuel pump, lighting, heater and air conditioning, turn signals, brake lights, power windows, gauges, wipers, radio, courtesy lighting, and power accessories.
Because fuse labels are abbreviated, the fuse list below expands the labels into their common circuit meanings.
Fuse list
The fuse-block labels most commonly shown for the Fiero are:
| Fuse / breaker label | Rating | Common meaning / circuit | Notes |
|---|---|---|---|
| ECM IGN | 10A | ECM / engine-control ignition feed | Engine control power |
| F PUMP | 10A | Fuel pump relay / oil pressure switch feed | Fuel pump circuit |
| TAIL | 20A | Tail lamps, parking lamps, side markers, license lamps | Exterior running lights |
| FAN E | 20A | Coolant fan relay, trunk blower | Cooling system |
| TURN B/U | 20A | Turn-signal and backup-lamp circuit | Signal / reverse-light related |
| TBI INJ1 | 5A | TBI injector circuit 1 | Four-cylinder engine-control related |
| STOP HAZ | 20A | Stop lamps and hazard flasher | Brake-light / hazard circuit |
| HTR/A/C | 25A | Heater / air-conditioning circuit | HVAC-related power |
| GAUGES | 10A | Gauges and related warning circuits | Instrument-related |
| TBI INJ2 | 5A | TBI injector circuit 2 | Four-cylinder engine-control related |
| BAT | 20A | Battery-fed accessory circuit | Exact loads can vary by year / equipment |
| WDO | 30A circuit breaker | Power windows | Power-window protection |
| INST LP | 5A | Instrument panel illumination lamps | Dash lighting |
| RADIO | 10A | Radio circuit | Radio power |
| PWR ACC | 30A circuit breaker | Power accessories | Often associated with power locks / rear defogger circuits depending on equipment |
| WIPER | 25A | Windshield wiper circuit | Wiper motor / related circuit |
| CTSY/LID | 25A | Courtesy / decklid-related circuit | Interior courtesy / rear compartment related |
Because Fieros were offered with different engines, trim levels, and options, the exact downstream loads can vary somewhat by year and equipment. The fuse-block labels themselves, however, are the most useful starting point for diagnosis.
Rear fuse-block connectors
The rear-view diagram shows connector cavity locations at the back of the fuse block.
The two brown rear connector locations are marked:
- IGN
- LP
These should be checked if there is evidence of heat damage, loose connections, poor previous repairs, or intermittent power loss through the fuse block.
Circuit breakers
The Fiero fuse block also uses circuit breakers.
The most obvious ones shown in the diagram are:
- WDO – 30A circuit breaker for the power-window circuit
- PWR ACC – 30A circuit breaker for power-accessory circuits
Unlike an ordinary fuse, a circuit breaker may reset after cooling, depending on type. This can cause an intermittent fault.
What the common abbreviations mean
Some Fiero fuse-block abbreviations are not immediately obvious:
| Abbreviation | Meaning |
|---|---|
| ECM IGN | Engine Control Module ignition feed |
| F PUMP | Fuel pump |
| HTR/A/C | Heater / air conditioning |
| TURN B/U | Turn signals / backup lamps |
| TBI INJ1 / INJ2 | Throttle-body injection injector circuits |
| STOP HAZ | Stop lamps / hazards |
| WDO | Power windows |
| INST LP | Instrument lamps |
| CTSY/LID | Courtesy / decklid circuit |
Relay-controlled circuits
Although the fuse block is under the dash, many Fiero circuits also use relays elsewhere in the car.
Important relay-controlled circuits include:
For some circuits, the fuse in the fuse block protects the control or supply side, while the actual load is switched by a relay located elsewhere in the car.
Examples:
- The F/PMP fuse is part of the fuel-pump circuit, but the actual pump is also controlled by the fuel-pump relay and oil-pressure-switch backup circuit.
- The HTR/A/C circuit is related to HVAC operation, but A/C and radiator-fan operation may also involve relays.
- The headlight system differs between 1984-1986 and 1987-1988 Fieros and should be diagnosed using the correct year-specific system information.
Related topics:
Common fuse-block problems
Common Fiero fuse and fuse-block problems include:
- Blown fuse
- Fuse installed with the wrong amperage
- Poor contact between fuse and fuse-block terminals
- Corrosion
- Heat damage
- Previous-owner wiring modifications
- Loose rear connector cavities
- Circuit breaker failure
- Repeatedly blown fuse caused by a short or failed component
A blown fuse should not simply be replaced repeatedly without finding the cause.
Diagnosis
When diagnosing a Fiero fuse or relay-related electrical problem:
- Identify the affected circuit.
- Check the correct fuse or circuit breaker.
- Verify the fuse rating.
- Check for power on both sides of the fuse.
- Inspect the fuse-block terminals for corrosion or looseness.
- Check the rear connector cavities if there is evidence of heat or intermittent power loss.
- If the circuit also uses a relay, test that relay and the related wiring.
- Inspect grounds.
- Inspect for aftermarket wiring or previous repairs.
A fuse that looks good visually may still have poor contact or may not be receiving power.
Repeatedly blown fuses
A fuse that blows repeatedly indicates a fault somewhere in the circuit.
Possible causes include:
- Short to ground
- Pinched or chafed wiring
- Failed motor
- Failed relay
- Failed switch
- Incorrect bulb or component
- Water intrusion
- Poor aftermarket wiring
Do not solve a repeatedly blown fuse by installing a higher-rated fuse.
Notes
This page is mainly a Fiero fuse-block overview.
For detailed circuit diagnosis, it is often better to continue to the specific circuit page, such as: