1991 Fuel Pump Relay Location: Your Essential Guide to Finding It Quickly and Safely

The fuel pump relay for most 1991 model year vehicles is primarily located within the vehicle's under-hood fuse and relay box, often on the driver's or passenger's side near the battery or firewall. Occasionally, it might be found inside the passenger compartment fuse panel, especially near the driver's lower dashboard area or the kick panels. Identifying the specific location for your 1991 car or truck requires consulting your owner's manual or a vehicle-specific repair manual. Look for a small, cube-shaped black or gray plastic component typically labeled as "Fuel Pump," "FP," "EEC," or sometimes identified by a circuit number like "#5" or "#9" in the fuse box diagram.

Understanding the exact location of your 1991 fuel pump relay is crucial if your vehicle cranks but won't start, or if you hear no humming sound from the fuel tank area when the ignition is turned on. A faulty relay is a common culprit behind fuel delivery problems. Knowing where it is saves valuable diagnostic time and money. This guide provides detailed information on common locations, how to identify the relay, testing procedures, safety precautions, and vehicle-specific considerations for finding and dealing with the fuel pump relay in 1991 vehicles.

Understanding the Role of the Fuel Pump Relay

Before diving into locations, grasp what the relay does. Its primary function is to act as an electrically controlled switch for the high-current fuel pump circuit. The fuel pump requires a significant amount of electrical power to operate. Running this heavy current directly through the ignition switch would cause excessive wear and potential overheating.

The fuel pump relay solves this problem. A low-current signal from the ignition switch or Powertrain Control Module (PCM) energizes the relay's small electromagnet coil. This magnetism pulls internal switch contacts together, completing the high-current circuit that powers the fuel pump. Essentially, the relay acts as an intermediary, allowing a small switch in the dashboard to control the powerful pump motor safely.

Symptoms of a failing relay include intermittent starting, the fuel pump not priming when the key is turned on, engine stalling while driving, or complete failure to start despite the engine cranking normally. Sometimes, a failing relay might cause a continuous buzzing sound.

Safety First: Critical Precautions

Working around automotive electrical systems requires caution. Follow these essential safety steps:

  1. Disconnect the Battery: ALWAYS disconnect the negative battery terminal before attempting to locate, test, or replace any relay or fuse. This prevents accidental short circuits, which can cause sparks, damage components, or even start an electrical fire. Set the disconnected terminal aside where it cannot accidentally touch the battery post.
  2. Fire Risk Awareness: The fuel system involves volatile gasoline. Have a suitable fire extinguisher readily available near your workspace. Never smoke or allow open flames near the vehicle during this or any fuel system work.
  3. Handling Relays: Relays can become warm during operation, but if you find one excessively hot or melted, that indicates a severe problem likely beyond just the relay itself. Avoid touching hot components.
  4. Avoid Bypassing: Never attempt to permanently "jump" or bypass the fuel pump relay using wires or paper clips. This defeats vital safety features, leaves the pump running continuously (a fire hazard), and often prevents the engine from running correctly as the PCM loses control of the pump circuit. Bypassing is strictly for diagnostic testing, as described later, and must be done temporarily and cautiously.
  5. Component Protection: Static discharge can damage sensitive electronic components. Handle relays and the PCM connectors carefully. Ground yourself by touching bare metal on the vehicle before touching electronic modules or connectors.
  6. Identify Correctly: Accidentally removing or testing the wrong relay can disable critical systems like the Engine Control Module (ECM/PCM), ignition, or radiator fans. Double-check identification before proceeding.

Primary Location: Under-Hood Fuse and Relay Box

For the vast majority of 1991 vehicles, this is the main area to search. It is usually a rectangular, black plastic box, often found in one of these positions:

  • Driver's Side Fender: Near the battery and the firewall.
  • Passenger's Side Fender: Close to the battery and the firewall.
  • Top Center near the Firewall: Behind the engine.
  • Directly on the Passenger's Side Fender: Clearly visible when opening the hood.

How to Find and Identify the Relay in the Under-Hood Box:

  1. Open the Hood: Secure it with the prop rod.
  2. Locate the Box: Identify the primary fuse/relay box in the positions mentioned.
  3. Remove the Cover: Plastic covers typically snap off or are held by small screws. Set the cover aside safely.
  4. Consult the Diagram: The inside of the cover or the box itself will have a diagram identifying each fuse and relay by name, function, or amperage rating. This diagram is your essential map. Match the fuse box layout to the diagram.
  5. Look for Labels: Manufacturers label the slots or the relays themselves. Common labels for the fuel pump relay include:
    • "Fuel Pump" (Most Common)
    • "FP"
    • "EEC" (Ford - This relay often powers the PCM and the fuel pump)
    • "Main" (Less common, often indicates a primary power relay that might include the pump)
    • A circuit number (e.g., "#5", "#9", "R1"). Refer to your diagram.
  6. Physical Appearance: The relay is typically a small cube or rectangle (approx 1" x 1" x 1.5") made of black or gray plastic. It has 4 or 5 metal prongs (terminals) protruding from the bottom that plug into sockets in the fuse box. Compare its shape and position to the diagram's markings. Relays are usually grouped together.
  7. Compare to Similar Relays: Many relays in the box look identical. This is why the diagram is critical. If unsure, note the position of suspected relays and compare them carefully to the diagram and any labels. Common identical-looking relays include the cooling fan relay, horn relay, and ECU/ECM power relay.

Secondary Location: Inside the Passenger Compartment Fuse Panel

While less common than the under-hood location for 1991 models, some vehicles place fuses and relays inside the cabin. Check here if you cannot locate it under the hood, especially after consulting resources specific to your model. Likely positions include:

  • Lower Dashboard (Driver's Side): Often below the steering column, above the pedals, or at the end of the dashboard. Sometimes covered by a small trim panel.
  • Kick Panel Area (Driver's or Passenger Side): The side areas where your feet rest near the door. Panels may snap off or require small screws removed.
  • Glovebox Area: Rare for this relay in 1991 models, but possible. Look behind the glovebox liner or on the side wall inside.

How to Find and Identify the Relay Inside:

  1. Access the Panel: Locate the compartment and remove its cover or access panel following the owner's manual or visual inspection for clips/screws.
  2. Use the Diagram: Inside the cover or panel will be a fuse/relay diagram. Use the same identification methods as for the under-hood box: look for "Fuel Pump," "FP," "EEC," or circuit numbers matching the diagram.
  3. Physical Identification: The relays look identical to those under the hood – small plastic cubes with metal prongs.

Finding Your 1991 Vehicle-Specific Relay Location

Knowing the general areas helps, but pinpointing it requires vehicle-specific information. Here's how:

  1. Owner's Manual: This is the first and most authoritative source. Check the index for "Fuses," "Relays," "Circuit Breakers," or "Fuel Pump." Refer to the diagrams provided. If you don't have it, search online for "[Your 1991 Make Model] owner's manual PDF."
  2. Factory Service Manual (FSM): The most accurate repair information. Search for "[Your 1991 Make Model] factory service manual PDF" or check automotive repair subscription services. FSMs detail the exact location, removal procedure, and circuit schematics.
  3. Reliable Online Repair Databases: Websites like AllDataDIY or Mitchell1 DIY (subscription-based) offer accurate, vehicle-specific repair info, including fuse/relay locations.
  4. Model-Specific Forums: Enthusiast forums dedicated to your specific 1991 car or truck are invaluable. Search for "1991 [Model] fuel pump relay location." Experienced owners and mechanics frequently share precise details and photos.
  5. Parts Store Lookup: Some major auto parts store websites allow you to view component locations. Search for a "1991 [Make] [Model] fuel pump relay" and see if a diagram is available.
  6. Video Tutorials: Search YouTube for "1991 [Make] [Model] fuel pump relay location." Visual guides can be very helpful, but ensure the source seems knowledgeable.

Common 1991 Models - Fuel Pump Relay Location Examples:

  • 1991 Ford F-Series/Bronco (Gasoline): Crucial Note: Uses an Inertia Safety Switch. The primary relay is typically labeled "EEC" in the under-hood fuse/relay box, often near the brake master cylinder or driver's side fender. The "EEC" relay powers the PCM and the fuel pump circuit, which runs through the inertia switch (usually located under the passenger side dashboard near the transmission hump or kick panel area) before reaching the pump.
  • 1991 GM (Chevy/GMC Truck, S-10/Blazer, Full-Size Cars like Caprice): Primarily located in the under-hood fuse/relay center. Labeled as "Fuel Pump" or "FP" relay. Positions vary but are common near the driver's side firewall. Check the diagram on the cover.
  • 1991 Chevrolet/GMC C/K Pickups & SUVs: Often found in the under-hood fuse/relay box, mounted near the driver's side fender or firewall.
  • 1991 Ford Mustang: Primarily in the under-hood fuse/relay box. Labeled "EEC" relay.
  • 1991 Toyota Pickup/4Runner: Located in the under-hood fuse/relay box, often labeled directly or identified by the diagram.
  • 1991 Honda Accord/Civic: Typically found in the under-hood fuse/relay box, likely near the battery or driver's side fender. Use the cover diagram to identify the specific slot labeled "Main" or "Fuel Pump."
  • 1991 Nissan Sentra/Stanza: Usually located in the under-hood fuse/relay box. Refer to the box diagram.

Always double-check with a resource specific to your exact year, make, model, and trim level. Engine type (gasoline vs. diesel) can also affect relay location.

Testing the 1991 Fuel Pump Relay

Before replacing the relay, testing helps confirm it's the problem. You'll need a basic multimeter.

Visual Inspection: While the vehicle battery is disconnected, remove the suspected fuel pump relay. Examine the plastic case for cracks, melting, or scorch marks. Smell for a burnt odor. Inspect the metal terminals for corrosion or signs of overheating.

Bench Testing (Relay Removed):

  1. Identify Terminals: Find the relay type (4-pin vs. 5-pin) and terminal markings. Common terminals: Control circuit - Two smaller terminals (usually labeled "85" and "86"). Load circuit - Two larger terminals (usually "30" and "87"). Some 5-pin relays have a second normally closed output ("87a") – ignore this for the fuel pump test.
  2. Resistance Test (Coil): Set multimeter to Ohms (Ω). Touch probes to terminals 85 and 86. You should get a moderate resistance reading (typically between 50Ω to 150Ω for the coil). Infinite resistance means an open coil (bad relay). Zero resistance means a shorted coil (bad relay).
  3. Resistance Test (Contacts - Open): Set multimeter to Ohms (Ω) or continuity (beep mode). Touch probes to terminals 30 and 87. The multimeter should read infinite resistance (open circuit), indicating the relay contacts are apart when unpowered.
  4. Activation Test: Apply 12V DC from a battery source (a small 12V battery or power supply) or from the vehicle battery using jumper wires. Connect POSITIVE (+) to terminal 86. Connect NEGATIVE (-) to terminal 85. You should hear and feel a distinct audible "CLICK" as the relay energizes.
  5. Resistance Test (Contacts - Closed): While keeping 12V applied to 85/86, quickly retest the resistance/continuity between terminals 30 and 87. The multimeter should now show very low resistance (close to 0Ω), meaning continuity. If the contacts don't close (no continuity) with power applied, the relay is faulty.

In-Vehicle Testing:

  1. Listen for Click: Have an assistant turn the ignition key to the "ON" position (do not crank). Place your hand on the relay. You should feel and hear a click as it energizes.
  2. Power Output Test (Terminal 87):
    • Disconnect the negative battery terminal (Safety!).
    • Carefully remove the relay.
    • Identify Terminal 87: Locate this output terminal within the relay socket. You'll probe into this socket contact.
    • Reconnect Battery.
    • Set multimeter to DC Volts (20V range).
    • Connect the BLACK (-) lead to a good ground (bare metal on engine or body).
    • Carefully probe the socket contact for Terminal 87 with the RED (+) lead. Turn ignition to ON.
    • No Voltage Expected: With ignition ON, you generally should not see battery voltage (12V) at terminal 87 unless the engine is running or the starter is actively cranking. This is because most vehicles only prime the pump for 1-2 seconds at key-on. Some vehicles require engine RPM signals to keep it powered. The absence of voltage here with the key only ON isn't conclusive proof of relay failure due to the prime cycle.
  3. Input Power Test (Terminal 30): Test the socket contact for Terminal 30. You should have battery voltage (approx. 12V) here at all times.
  4. Control Voltage Test (Terminal 86): Test the socket contact for Terminal 86. When the ignition is turned to ON (and potentially during cranking), you should have battery voltage (approx. 12V) here relative to ground.
  5. Ground Test (Terminal 85): Test the socket contact for Terminal 85. Check for continuity between this socket contact and ground using the multimeter's continuity function (ensure battery is disconnected first!). You should have good continuity. If not, there's a ground circuit problem.
  6. Swap Test: If a relay of the exact same type and specifications is used for another function (like the horn or cooling fan) that is known to work, you can swap the suspected fuel pump relay with this known good relay (after confirming they are identical). Turn the key to ON or attempt to start the vehicle. If the fuel pump problem disappears and the other function stops working, the original relay is bad. If the fuel pump issue persists, the problem lies elsewhere (PCM command, wiring, inertia switch, pump itself).

The Diagnostic Jumper Method (For Professional Understanding - Use Extreme Caution):

  1. DISCONNECT THE BATTERY NEGATIVE TERMINAL FIRST.
  2. Remove the fuel pump relay.
  3. Identify terminal sockets 30 (Constant Battery Power) and 87 (Output to Fuel Pump) in the relay socket.
  4. Temporarily and very carefully, insert a fused jumper wire (use a fuse appropriate for the fuel pump circuit, typically 15-20 amps) between these two sockets in the relay box. This bypasses the relay and provides direct power to the fuel pump circuit. NEVER use a paperclip or unfused wire.
  5. Reconnect the battery.
  6. Observe: The fuel pump should run continuously when the jumper is installed (and the battery is connected), regardless of ignition position.
    • If the pump runs: This proves the wiring and pump motor itself are functional downstream of the relay socket. It strongly indicates a problem with the relay or its control circuit (power to relay coil - terminal 86, ground path - terminal 85, or PCM signal failure to trigger the relay).
    • If the pump does not run: The problem lies downstream of the relay socket: the inertia switch (if equipped), wiring to the pump, or the pump itself.
  7. REMOVE THE JUMPER WIRE IMMEDIATELY after testing. Do NOT attempt to start the engine with this jumper installed long-term, as it defeats the PCM's ability to control the pump and is a safety hazard.

Replacing a Faulty 1991 Fuel Pump Relay

  1. Purchase Correct Replacement: Relays are vehicle-specific by terminal configuration and electrical specifications. Take the old relay to the auto parts store to ensure an exact match. Do not guess.
  2. Disconnect Battery: Crucial step - disconnect negative terminal.
  3. Remove Old Relay: Firmly grasp it and pull straight out. Rocking gently side-to-side might help free it.
  4. Inspect Socket: Check the relay socket terminals for corrosion, bending, or signs of melting. Clean corrosion with electrical contact cleaner and a small brush if needed.
  5. Install New Relay: Align the new relay's prongs correctly with the socket (note the shape - one pin may be offset) and push firmly straight down until it seats fully.
  6. Reconnect Battery:
  7. Test:
    • Turn the ignition to ON. Listen for the fuel pump to prime for 1-2 seconds.
    • If it primes, crank the engine. If it starts and runs normally, the relay replacement was likely successful.
    • Take a short test drive to ensure the problem doesn't reoccur under different conditions (like a bump triggering a bad connection).

When Replacement Doesn't Fix the Problem

If you've replaced a confirmed-bad relay and the fuel pump still doesn't work:

  1. Review Testing: Double-check your earlier testing steps. Did you misdiagnose the relay? Confirm voltage at socket terminal 30 (always hot). Confirm voltage at socket terminal 86 (ON) and ground at 85 (disconnect battery to test continuity) were present? Did the pump run with a diagnostic jumper? This process helps identify the next diagnostic step.
  2. Check Fuses: Even with a good relay, a blown fuse (often also in the under-hood box) will prevent power from reaching the relay or pump. Find the fuse related to the fuel pump circuit using the box diagram. Test it visually (broken wire inside) or with a multimeter (continuity across the blades). Replace a blown fuse with the identical rating.
  3. Inspect Wiring: Look for damaged, frayed, pinched, or corroded wires leading to and from the relay socket, the inertia switch, and the fuel pump. Check connections at all points. Corrosion at connectors near the fuel tank is common. Repair damaged wiring properly.
  4. Test the Inertia Switch (Ford): Press the reset button on the Ford inertia switch (if equipped). Test for continuity through the switch using a multimeter (with battery disconnected). If open circuit even after resetting, the switch is faulty. Bypassing it temporarily (joining the two wires on its connector) for testing can confirm pump operation, but never drive the vehicle without a functioning inertia switch - it's a critical safety device designed to shut off the pump during a collision.
  5. Test the Fuel Pump: Confirm the pump is receiving power at its electrical connector (using multimeter or a test light) when it should be running (during prime or cranking). If power arrives but the pump doesn't run, the pump motor is likely bad. If no power arrives at the pump, trace back upstream (inertia switch, wiring).
  6. PCM/ECM Signal Issue: The PCM might not be commanding the relay to energize. This could be due to a faulty PCM, a failed input sensor preventing the engine from starting (e.g., crank sensor), or a wiring issue between the PCM and relay socket terminal 86. Professional diagnosis with a scan tool is typically needed at this level.

Conclusion

Locating the fuel pump relay in a 1991 vehicle typically involves checking the under-hood fuse and relay box first, using the diagram on the cover to identify the relay labeled "Fuel Pump," "FP," "EEC," or its specific circuit number. Failing that, check the interior fuse panels near the driver's knees or kick panels. Rely on the owner's manual or vehicle-specific resources for precise confirmation. Once found, understanding how to test the relay using basic tools allows you to confirm its functionality as part of diagnosing a non-starting or fuel delivery issue. Safety is paramount: always disconnect the battery before handling relays or wiring, and never permanently bypass the relay or disable safety devices like the inertia switch. By methodically finding, testing, and if necessary, replacing the fuel pump relay with the correct part, you can often restore your 1991 vehicle's operation without the need for immediate costly professional help. Remember, if troubleshooting beyond the relay points to the fuel pump, wiring, or PCM, professional assistance may be required.

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