Fuses and relays
Fuses and relays refers to the electrical protection and control devices used in the Pontiac Fiero.
Fuses protect electrical circuits from excessive current. Relays allow a low-current control circuit to switch a higher-current load such as a fan, fuel pump, or other electrical device.
Overview
The Pontiac Fiero uses fuses, fusible links, circuit breakers, and relays throughout the electrical system.
These parts are important for diagnosis because many electrical problems are caused by blown fuses, poor fuse-panel contacts, failed relays, damaged fusible links, bad grounds, or wiring faults.
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Location
Image wanted: Photo showing the Fiero interior fuse panel and common relay locations, preferably with labels or arrows.
The main fuse panel is located inside the passenger compartment.
Relays are located in several areas depending on circuit and model year. Some relays are located in the front compartment, some in the rear engine compartment, and some near the devices they control.
Because relay locations and circuit details can vary by model year and equipment, the correct wiring diagram should be checked before diagnosis.
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Fuses
A fuse is a protective device designed to open the circuit if current becomes too high.
If a fuse blows, it usually means one of the following:
- The circuit was overloaded
- A wire or component shorted to ground
- The wrong fuse rating was installed
- A component failed internally
- Wiring was damaged
- Previous repairs or modifications caused a fault
A blown fuse should not simply be replaced repeatedly without finding the cause.
Fuse ratings
Fuses are rated by amperage.
The replacement fuse should match the correct rating for the circuit. Installing a larger fuse than specified can allow wiring or components to overheat before the fuse opens.
A higher-rated fuse should not be used as a “fix” for a fuse that keeps blowing.
Fusible links
The Fiero also uses fusible links.
A fusible link is a short section of special wire designed to act as circuit protection for higher-current circuits. Fusible links are commonly used near main power feeds and charging-system wiring.
A failed fusible link can cause major electrical problems, including loss of power to several circuits.
Possible symptoms of a failed fusible link include:
- No power to multiple circuits
- No-start condition
- Charging-system problems
- Dead electrical system in one area of the car
- Intermittent power loss if the link or connection is damaged
Fusible links should be repaired using the correct type and gauge of fusible-link wire, not ordinary wire.
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Circuit breakers
Some circuits may use circuit breakers instead of ordinary fuses.
A circuit breaker can open when overloaded and may reset after cooling, depending on type. This can cause an intermittent electrical problem where a circuit works, stops working, and later works again.
Circuit breakers are commonly used where temporary overloads can occur, such as motor-driven circuits.
Relays
A relay is an electrically operated switch.
Relays allow a low-current circuit to control a higher-current load. This keeps heavy current out of switches and control modules.
A typical relay circuit includes:
- Battery or ignition power
- Ground
- Control signal
- Relay coil
- Relay contacts
- Output to the controlled device
A failed relay can cause a device not to operate even when the fuse is good.
Common Fiero relays
Common relay-controlled systems on the Fiero include:
- Fuel pump
- Radiator fan
- Headlights
- Air conditioning
- Horn
- Rear window defogger, where equipped
- Other electrical accessories depending on model and options
Relay locations and designs should be verified using the correct year wiring information.
Fuel pump relay
The fuel pump relay controls power to the electric fuel pump.
A failed fuel pump relay can cause a no-start condition or a delayed-start condition. However, the Fiero fuel pump circuit also has backup behavior through the oil pressure switch on many applications, so diagnosis should not rely on the relay alone.
Possible symptoms of fuel pump relay problems include:
- No fuel pump prime
- Extended cranking before start
- No-start condition
- Intermittent fuel pump operation
- Fuel pump works only after oil pressure builds
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Radiator fan relay
The radiator fan relay controls the radiator fan motor.
The relay is part of the higher-current fan motor circuit. It is controlled by the fan switch, air-conditioning system, or related control circuit depending on year and configuration.
A failed fan relay can cause the radiator fan not to run even if the fan motor itself is good.
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Headlight relays and modules
The Fiero headlight system differs between early and late model years.
1984-1986 Fieros use the first-generation headlight motor system.
1987-1988 Fieros use the second-generation headlight system with a different control design.
Because the systems are different, relay and control diagnosis should be matched to the correct model year.
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Horn relay
The horn circuit uses a relay so the horn switch does not carry the full horn current.
A horn problem may be caused by the fuse, relay, horn switch, horn itself, wiring, or ground.
Possible symptoms include:
- Horn does not work
- Horn works intermittently
- Horn sounds weak
- Horn stays on
- Clicking relay but no horn sound
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Relay testing
Relay diagnosis usually involves checking both the control side and the load side of the circuit.
Basic checks include:
- Check the related fuse.
- Identify the correct relay.
- Check for power at the relay.
- Check for ground where required.
- Check whether the relay receives a control signal.
- Listen or feel for relay clicking.
- Check whether power leaves the relay when activated.
- Test or swap with a known-good relay only when the relay type and circuit are correct.
- Check the controlled device separately.
- Check wiring and grounds.
A relay that clicks is not always good. The internal contacts may still be burned, weak, or unable to carry current.
Fuse testing
A fuse can sometimes look good visually but still be faulty or have poor contact.
Useful checks include:
- Visual inspection
- Test light check on both sides of the fuse
- Multimeter continuity check
- Voltage check under load
- Fuse-panel contact inspection
- Checking for corrosion or heat damage
The most useful in-car test is often to check for power on both sides of the fuse while the circuit should be powered.
Repeatedly blown fuses
A fuse that blows repeatedly indicates a fault.
Possible causes include:
- Short to ground
- Damaged wiring
- Failed motor
- Failed relay or switch
- Incorrect bulb or component
- Incorrect fuse rating
- Aftermarket wiring fault
- Water intrusion
- Chafed wire
- Pinched wire after repair work
Do not install a larger fuse to stop a fuse from blowing. The correct repair is to find and fix the cause of the excessive current.
Intermittent electrical problems
Fuse and relay problems can be intermittent.
Possible causes include:
- Loose fuse-panel contacts
- Corrosion
- Heat-related relay failure
- Vibration-sensitive connection
- Loose relay socket
- Damaged wiring
- Weak ground
- Poor previous repair
- Fuse that loses contact in the panel
Intermittent problems should be diagnosed by checking power and ground while the fault is present, when possible.
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Aftermarket wiring
Many Fieros have had aftermarket radios, alarms, amplifiers, lighting, gauges, engine swaps, or other electrical accessories installed.
Aftermarket wiring can cause fuse and relay problems if it is poorly installed.
Common problems include:
- Incorrect power source
- No fuse protection
- Oversized fuse
- Poor ground
- Scotch-lock or crimp connector failure
- Wires routed near sharp edges
- Wires routed near heat
- Added load on an existing circuit
- Removed or bypassed factory protection
Aftermarket circuits should be inspected when diagnosing unexplained fuse failures or electrical problems.
Diagnosis
Basic fuse and relay diagnosis includes:
- Identify the affected circuit.
- Check the correct fuse.
- Verify the fuse rating.
- Check for power on both sides of the fuse.
- Check the related relay, if equipped.
- Check for relay control power and ground.
- Check relay output.
- Check the controlled device.
- Check wiring between the fuse, relay, switch, and load.
- Check grounds.
- Inspect for previous repairs or modifications.
- Use the correct wiring diagram for the model year.
Diagnosis should be circuit-specific. Guessing and replacing parts can miss wiring faults, poor grounds, or incorrect previous repairs.
Common mistakes
Common mistakes during fuse and relay diagnosis include:
- Replacing a blown fuse without finding the cause
- Installing a higher-rated fuse
- Assuming a relay is good because it clicks
- Testing only the fuse and not the circuit
- Ignoring grounds
- Ignoring fusible links
- Assuming all model years are wired the same
- Swapping relays without confirming pin layout
- Overlooking aftermarket wiring
- Overlooking corrosion or loose terminals
Service notes
When working on fuses and relays:
- Use the correct fuse rating.
- Do not bypass fuses.
- Do not replace fusible links with ordinary wire.
- Disconnect the battery when working on major wiring repairs.
- Use wiring diagrams for the correct model year.
- Check grounds as well as power feeds.
- Inspect relay sockets and fuse-panel contacts.
- Label added wiring when possible.
- Repair damaged wiring properly.
- Protect wiring from heat, sharp edges, and moving parts.
Notes
Fuses and relays are simple parts, but they are part of larger circuits.
A blown fuse, failed relay, or bad fusible link is often a symptom of another problem. Good diagnosis should look at the fuse or relay, the wiring, the load, the switch or control circuit, and the ground path.
Forum discussions
Useful repair or diagnostic threads may be added here when they contain practical fuse, relay, or electrical troubleshooting information.