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

Fiero 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 / Computer Command Control ignition feed	Engine-control ignition power
F PUMP	10A	Fuel pump relay / oil pressure switch feed	Fuel pump circuit
TAIL	20A	Tail lamps, parking lamps, side marker lamps, license plate lamp, and related illumination	Exterior running lights and related illumination
FAN E	20A	Coolant fan relay coil; engine/trunk blower on earlier V6 cars where equipped	Cooling fan control circuit; verify by model year
TURN B/U	20A	Turn-signal flasher and backup lamps	Signal / reverse-light related
TBI INJ1	5A	Throttle-body injection injector circuit 1	Four-cylinder engine-control related
STOP HAZ	20A	Stop lamps, hazard flasher, and warning chime	Brake-light / hazard circuit
HTR/A/C	25A	Heater / air-conditioning circuit	HVAC-related power
GAUGES	10A	Gauges and related warning/control circuits	Instrument-related circuits
TBI INJ2	5A	Throttle-body injection injector circuit 2	Four-cylinder engine-control related
BAT	20A	Battery-fed circuit	Constant-power feed for related circuits
WDO	30A circuit breaker	Power windows	Power-window protection
INST LP	5A	Instrument panel lamps and headlight warning	Dash lighting / warning circuit
RADIO	10A	Radio and related control circuits	Radio, cruise control, VSS/TCC-related circuits depending on equipment
PWR ACC	30A circuit breaker	Power door locks and rear window defogger	Power accessory circuit
WIPER	25A	Windshield wiper circuit	Wiper motor / related circuit
CTSY/LID	25A	Courtesy lights, rear compartment light, rear lock relay, and power sport mirror control	Interior courtesy / rear compartment / power mirror-related circuit

Because Fieros were offered with different engines, trim levels, and options, the exact downstream loads can vary by year and equipment. The fuse-block labels themselves are usually the most useful starting point for diagnosis.

Power distribution and fusible links

The fuse block is only one part of the Fiero power distribution system.

The 1988 service manual describes the power distribution system as including:

• Fusible links
• Fuses
• Circuit breakers
• Light switch
• Ignition switch

Fusible links are short protective wire sections used on higher-current feed circuits. They are intended to melt and stop current flow if excessive current occurs in a part of the electrical system that is not protected by ordinary fuses or circuit breakers.

Fusible links should not be replaced with ordinary wire.

The 1988 service manual lists several fusible-link locations, including fusible links at the battery junction block, forward lamp harness, starter solenoid, and rear bulkhead connector. Exact fusible-link identification should be checked against the correct model-year wiring diagram.

Related topics:

• Electrical system
• Wiring diagrams
• Connector pinouts

Rear fuse-block connectors

Some service information shows rear connector cavity locations at the back of the fuse block.

These rear connections can be relevant when diagnosing intermittent power loss, heat damage, loose terminals, or previous wiring repairs.

If rear fuse-block connector work is required, use the correct model-year wiring diagram and connector-location information. Do not rely only on the front fuse-block label.

Circuit breakers

The Fiero fuse block also uses circuit breakers.

The most obvious circuit breakers shown in the fuse-block diagram are:

• WDO – 30A circuit breaker for the power-window circuit
• PWR ACC – 30A circuit breaker for power-accessory circuits

The owner's manual also notes that some circuits use circuit-breaker protection instead of an ordinary fuse. Examples include headlight wiring and the windshield wiper motor.

Unlike an ordinary fuse, a circuit breaker may open during an overload and later reset. This can create an intermittent problem where a circuit stops working, then works again after the breaker cools.

If a circuit breaker repeatedly opens, the cause of the overload should be found rather than bypassing the protection.

Flasher and relay locations

The fuse block protects many circuits, but several flashers and relays are located elsewhere.

The owner's manual identifies these under-dash locations:

• The hazard flasher and horn relay are located under the right side of the instrument panel.
• The turn-signal flasher is located on the left side of the steering column, under the instrument panel.

The 1988 service manual gives additional component locations, including:

• Fuse block — behind the left side of the instrument panel
• Coolant fan relay — left front corner of the front compartment
• Fuel pump relay — engine compartment, left side of the rear bulkhead
• A/C power relay — front compartment, on the right side of the heater/A/C module
• High-speed blower relay — on the right side of the heater/A/C plenum

These locations are useful starting points, but relay locations and wiring details should still be verified against the correct model-year wiring diagram.

Related topics:

• Fuel pump relay
• Radiator fan relay
• Headlight control module
• Horn
• Air conditioning

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

The fuse block protects many circuits, but the actual relay for a circuit may be located somewhere else in the car.

Important relay-controlled circuits include:

• Fuel pump
• Radiator fan
• Headlights
• Horn
• Air conditioning

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:

• Fuel pump relay
• Radiator fan relay
• Headlight control module
• Headlight motor problems

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:

1. Identify the affected circuit.
2. Check the correct fuse or circuit breaker.
3. Verify the fuse rating.
4. Check for power on both sides of the fuse.
5. Inspect the fuse-block terminals for corrosion or looseness.
6. Check the rear connector cavities if there is evidence of heat or intermittent power loss.
7. If the circuit also uses a relay, test that relay and the related wiring.
8. Inspect grounds.
9. 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:

• Fuel pump
• Radiator fan
• Headlights
• Horn
• Air conditioning
• Electrical system

See also

• Electrical system
• Ground problems
• Wiring diagrams
• Connector pinouts
• Fuel pump
• Fuel pump relay
• Radiator fan
• Radiator fan relay
• Headlights
• Headlight motor problems
• Headlight control module
• Horn
• Air conditioning
• No-start diagnosis
• Fuse block
• Circuit breakers
• Hazard flasher
• Turn signal flasher
• Power distribution
• Fusible links