1999 Ford Explorer Fuel Pump Relay: Location, Symptoms, Testing & Replacement Guide

The fuel pump relay is a critical but often overlooked component in your 1999 Ford Explorer. When it fails, your SUV won't start or run. This guide provides the definitive explanation of its location, the symptoms of failure, how to test it, and a simple replacement process you can do yourself.

What the Fuel Pump Relay Does & Why It Matters
The fuel pump relay acts as a heavy-duty switch controlled by your Explorer's Powertrain Control Module (PCM). Your fuel pump requires significant electrical current to operate. The PCM cannot handle this current directly. Instead, it sends a small signal to the fuel pump relay. The relay responds by closing a set of internal contacts, allowing full battery power to flow directly to the fuel pump motor. This happens every time you turn the key to the "Run" or "Start" position. Without a functioning relay, the fuel pump receives no power, meaning no fuel pressure reaches the engine. The result is a vehicle that cranks but will not start and run.

1999 Ford Explorer Fuel Pump Relay Location
The fuel pump relay on a 1999 Ford Explorer is located inside the Central Junction Box (CJB), also commonly referred to as the power distribution box or main fuse box. This black plastic box is situated in the engine compartment, on the driver's side. It is mounted on the vehicle's inner fender liner, near the battery and the brake master cylinder.

  1. Identify the CJB: Open the hood. Locate the large, rectangular, black plastic box directly in front of the driver's position, towards the back of the engine compartment near the firewall/fender.
  2. Remove the Cover: Lift the cover straight up. It is held on by tabs or small clips.
  3. Identify the Relay: The cover will have a diagram or label identifying each relay and fuse position. Look specifically for "Fuel Pump," "FP," or "Relay 13." On the 1999 Explorer, the fuel pump relay is traditionally Relay 13. It is a standard ISO mini relay, usually black or grey plastic cube, about 1.5 inches square. Identify it using the diagram on the underside of the CJB cover. Note: If the cover diagram is missing or faded, Relay 13 is typically found near the top or side of the box, towards the engine side.

Symptoms of a Bad Fuel Pump Relay in a 1999 Explorer
Failure of the relay prevents power from reaching the fuel pump, leading to several specific symptoms:

  1. Engine Cranks But Won't Start: This is the most common symptom. The starter motor turns the engine over normally, but there is no fuel reaching the engine, causing it to fail to start.
  2. Engine Stalls Suddenly While Driving: A failing relay might cut power to the fuel pump while the engine is running, causing an immediate and unexpected stall. The engine will likely restart after cooling down briefly (sometimes called "heat soak" failure), mimicking a bad fuel pump.
  3. Intermittent Starting Problems: The vehicle might start fine one time and fail the next. Or, after driving and the engine is warm, it may refuse to restart (heat-related relay failure).
  4. No Fuel Pump Prime Noise: When you first turn the key to the "Run" position (before cranking), you should hear a distinct electric "whirring" or "buzzing" sound from under the rear of the vehicle (the fuel tank area) lasting 1-3 seconds. This is the fuel pump priming the system. No noise at all when turning the key to "Run" strongly suggests a problem with the fuel pump circuit – the relay, its fuse, or the pump itself.
  5. Clicking Sound from CJB: Sometimes, a physically failing relay might produce a rapid clicking sound from the CJB when turning the key to "Run" or "Start" – an indication the internal contacts are failing to engage properly.

Testing the 1999 Explorer Fuel Pump Relay
Testing helps confirm the relay is faulty before replacement.

  • Simple Swap Test: The most practical test is often swapping the suspect fuel pump relay with another identical relay in the CJB that controls a non-essential system (like the horn relay - Relay 11 - or rear window defogger relay - Relay 7 - check the CJB cover diagram to confirm identical relays). Remove Relay 13 (Fuel Pump) and Relay 11 (Horn). Swap their positions. Turn the key to "Run"; listen for the fuel pump prime sound and test the horn button. If the horn now doesn't work and the fuel pump primes (and the engine starts), the original Relay 13 is bad. If the horn works but the fuel pump still doesn't prime, the problem is likely elsewhere (fuse, pump, wiring). If both systems now work, it was likely just a poor connection.
  • Multimeter Test (Ohms - Coil):
    1. Remove the relay from the CJB.
    2. Set your multimeter to Ohms (Ω), typically the 200Ω range.
    3. Identify the relay coil terminals. Most ISO mini relays follow standard pin designations (often molded into the plastic base). Terminals 85 and 86 are for the relay coil.
    4. Place multimeter probes on terminals 85 and 86.
    5. A good relay coil will typically measure 50-120 Ohms. If it shows infinite resistance (OL or Over Limit) or 0 Ohms, the coil is faulty and the relay is bad.
  • Multimeter Test (Continuity - Contacts):
    1. Set multimeter to Continuity (diode symbol or beeper mode).
    2. Identify the switched contact terminals: Terminal 30 is power input (common), Terminal 87a is Normally Closed (NC), Terminal 87 is Normally Open (NO). The fuel pump relay uses the NO path (30 to 87).
    3. Place probes on Terminals 30 and 87a. There should be continuity (beep) when the relay is not activated.
    4. Place probes on Terminals 30 and 87. There should be no continuity initially.
    5. Activating the Coil: Apply 12 volts to pins 85 and 86 (e.g., positive from a 9V battery to 85, negative to 86). Do not apply power for more than a few seconds.
    6. With the coil powered:
      • Terminals 30 to 87a: Continuity should be broken (open circuit).
      • Terminals 30 to 87: Continuity should be established (closed circuit).
    7. If the contacts do not change state correctly when powered, or remain stuck open/closed even without power, the relay is bad.
  • Listen for Click: While powering the coil (pins 85 & 86 with 12V), you should hear and feel a distinct "click" inside the relay as the contacts move. A silent relay when powered likely has a bad coil.

How to Replace the 1999 Ford Explorer Fuel Pump Relay
Replacement is straightforward once you locate it.

Tools Needed: Phillips screwdriver (if needed for CJB cover), replacement ISO mini relay (Ford part # F57B-14B192-AA, 5W4Z-14B192-AA, or Motorcraft part # DY-1048).

  1. Turn Ignition Off: Ensure the key is in the OFF position.
  2. Open CJB: Remove the cover of the Central Junction Box in the engine compartment (as described above).
  3. Locate Relay 13: Identify the Fuel Pump Relay (Relay 13) using the diagram.
  4. Remove Old Relay: Firmly grasp the old relay and pull it straight up and out of its socket. Apply even pressure; wiggling slightly may help if it's tight.
  5. Inspect Socket: Quickly check the relay socket for any signs of corrosion, melting, or bent pins. Clean gently with electrical contact cleaner if corroded. Do not bend pins.
  6. Install New Relay: Align the pins on the new relay with the holes in the socket (it only fits one way). Press down firmly and evenly until it seats completely. Ensure it is fully seated and flush with the other relays.
  7. Test: Turn the ignition key to the "Run" position (do not start). Listen for the fuel pump priming sound (1-3 seconds of buzzing/whirring from the rear). Turn the key back to "Off". If you hear the sound, installation is likely correct.
  8. Replace CJB Cover: Securely snap the cover back onto the CJB.
  9. Final Check: Attempt to start the engine. If the relay was the issue, the engine should now start normally.

Common Questions & Troubleshooting

  • Where to Buy the Replacement Relay? Auto parts stores (AutoZone, O'Reilly, Advance Auto Parts, NAPA), Ford dealership parts counter, or online retailers (RockAuto, Amazon). Standard ISO mini relays are inexpensive (25). Ensure it's labeled for fuel pump or general automotive use and matches the part numbers above.
  • Is it the Relay or the Fuel Pump? The swap test (swapping with horn relay) is the best initial diagnostic. No fuel pump prime sound points strongly to the circuit (relay, fuse). If the relay tests good and you hear the prime sound but it cranks and won't start, the pump may still be bad or there could be pressure/filter issues. If the pump gets noisy before failure, that points more directly to the pump itself.
  • What About the Fuel Pump Fuse? The fuel pump circuit has a fuse protecting its power supply. In the CJB, locate the 20 Amp fuse, traditionally Fuse # 11 (or # 10, check CJB diagram for "Fuel Pump" or "FP"). Always check this fuse first if you have no pump prime noise and suspect the relay. A blown fuse needs replacement, but also investigate why it blew (short circuit, pump motor failure). Replace with only the same amperage fuse.
  • What if the New Relay Doesn't Fix It?
    • Recheck the Fuse: Is Fuse #11/10 intact?
    • Confirm Fuel Pump Prime: Are you absolutely sure you don't hear the pump run for a few seconds at "Run"? Have someone listen near the fuel tank area.
    • Check Inertia Switch: The 1999 Explorer has a fuel pump shut-off (inertia) switch, usually located in the passenger footwell behind the kick panel or under the dash behind the glovebox. If tripped (often from a bump or accident), it cuts power to the pump. Press the button on the top to reset it.
    • Check Wiring & Grounds: Look for damaged wires leading to the CJB, fuel pump, or PCM. Check for corroded ground connections (especially G101, a major ground near the battery/CJB). Requires more advanced diagnostics.
    • Test Fuel Pressure: Requires a gauge. Measures if the pump can actually build pressure, even with power. Low/no pressure points to a weak/dead pump or pressure regulator.
    • PCM Signal Check: Verify the PCM is actually sending the signal to activate the relay (requires multimeter at CJB socket pin 85 or 86 or scan tool access). Indicates if there's a control system issue.
    • The Fuel Pump: If all else checks out (power at the pump harness connector when it should be, good ground, inertia switch reset), the fuel pump itself is likely faulty.
  • Is There a Recall for the 1999 Explorer Fuel Pump Relay? Ford did not issue a general recall specifically for the fuel pump relay itself on 1999 Explorers. However, like any electromechanical component, relays eventually wear out and are a common failure point with age.
  • Relay Compatibility: Can I use any ISO mini relay? Yes, any automotive-grade ISO mini relay rated for at least 20A switching (many handle 30-40A) is electrically compatible. Standardizing on the Motorcraft DY-1048 is recommended, but equivalents are readily available. Do not use a relay with lower current capacity.

Prevention and Reliability
While relays can't last forever, their service life is long. Avoid exposing the CJB to excessive moisture. Using dielectric grease sparingly on the relay pins when installing can help prevent corrosion and ensure good contact over time. Carrying a spare relay and fuse in the glovebox is a cheap and wise precaution for older vehicles, as relay failure can happen suddenly and leave you stranded. Addressing any electrical issues promptly (like flickering lights, hard starts) can prevent undue stress on the CJB components.

Conclusion
A failed fuel pump relay is a common cause of no-start conditions on the 1999 Ford Explorer. Its location in the engine compartment's Central Junction Box (Relay 13) makes diagnosis and replacement relatively simple. Recognizing the key symptom – the engine cranks but fails to start, accompanied by no fuel pump priming sound – points directly to the relay circuit. Performing the relay swap test with an identical relay (like the horn relay) is a quick diagnostic. Confirming the fuse (Fuse #11/10) is good is also essential. Replacement involves pulling out the old relay and pushing in a new standard ISO mini relay. Understanding this critical component and its straightforward fix can save you time, money, and the frustration of being stranded. Always prioritize safety when working around vehicle electrical systems. If unsure about diagnosis or replacement steps, consult a qualified mechanic.

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