99 Ford Ranger Fuel Pump Relay: Your Essential Fix Guide for No-Start Issues

If your 1999 Ford Ranger cranks over but refuses to start, a faulty fuel pump relay is one of the most common and critical culprits you should investigate immediately. This small, inexpensive relay controls power to your truck's electric fuel pump. When it fails, the pump doesn't run, starving the engine of fuel no matter how much you crank. Understanding its location, function, symptoms of failure, and how to test and replace it is fundamental knowledge for any 99 Ranger owner. Ignoring a bad relay wastes time and battery life; diagnosing it correctly gets you back on the road fast.

The Critical Role of the Fuel Pump Relay in Your 99 Ranger

The fuel pump relay acts as a high-amperage switch controlled by a low-amperage signal from the Powertrain Control Module (PCM). When you turn the ignition key to the "Run" position, the PCM sends a ground signal to the relay for a few seconds, energizing its coil. This coil pulls internal contacts together, completing the circuit that sends full battery power to the electric fuel pump submerged in the fuel tank. This primes the fuel system. When you crank the engine, the PCM continues supplying the ground signal, keeping the pump running. Once the engine starts, the PCM maintains the signal as long as it detects engine rotation. The relay handles the heavy electrical load required by the pump, protecting the delicate PCM circuitry. Without this relay functioning correctly, the pump gets zero power, and the engine gets zero fuel, leading directly to a crank-no-start condition. Its failure is often sudden and complete.

Exact Location: Finding the Relay Box in Your 99 Ranger

Locating the relay is the first practical step. Forget the passenger footwell on this model year. For the 1999 Ford Ranger, the Power Distribution Box housing the fuel pump relay resides under the hood. Open the hood and look towards the driver's side fender, near the brake master cylinder and the firewall. You will see a large black plastic box, typically the size of a small lunch box, serving as the main power distribution center. The lid of this box is usually labeled with a diagram or a chart indicating which fuse or relay occupies each slot. The fuel pump relay in a 99 Ranger is almost universally found in position number 8 within this box. Refer to the lid diagram to confirm slot 8 is designated for the fuel pump relay before proceeding. Be aware that a similar-sized relay, the PCM power relay (sometimes called the EEC relay), is located nearby, often in slot 2 or slot 5. Mistaking these can lead to frustration – ensure you have the correct slot. Look for "F/PMP" or similar labeling on the lid chart.

Unmistakable Symptoms of a Faulty Fuel Pump Relay

Recognizing signs pointing directly to the relay helps focus your diagnostics:

  1. Engine Cranks Normally but Will Not Start: This is the hallmark symptom. The starter engages and spins the engine, but it never fires up. No sputtering, no coughing, just endless cranking without ignition. It mimics a complete lack of fuel pressure.
  2. No Audible Fuel Pump Hum: During the initial key-on phase before cranking, a healthy fuel pump emits a distinct humming or buzzing sound for 1-2 seconds from the rear of the truck (near the fuel tank). If you turn the key to "Run" and hear absolutely nothing from the back, the pump isn't receiving power, and the relay is a prime suspect. Listen carefully near the fuel filler neck or underneath the truck near the tank.
  3. Sudden Failure During Operation: While less common than failing during start-up, the relay can fail while driving. The engine will immediately stall and refuse to restart, leaving you stranded. There's typically no warning, just a sudden shutdown.
  4. Intermittent Starting Issues: A relay with failing internal contacts might cause random no-start problems. The truck might start perfectly fine one minute, then refuse to start the next, only to start again later without any obvious trigger. Tapping or wiggling the relay temporarily restoring function is a classic sign of internal contact failure.
  5. Check Engine Light May or May Not Be On: While relay failure itself usually doesn't trigger a specific Check Engine Light code directly related to the relay, issues like low fuel pressure caused by the non-functional pump (due to no relay signal) can sometimes set codes like P0190 (Fuel Rail Pressure Sensor Circuit Malfunction) or P0230 (Fuel Pump Primary Circuit Malfunction), though these are not guaranteed. A lack of codes does not rule out the relay.

Step-by-Step Guide: Testing Your 99 Ranger Fuel Pump Relay

You need only basic tools to effectively test the relay: a digital multimeter and a simple jumper wire (a short piece of wire with alligator clips on each end is ideal). Before testing anything electrical on the truck, disconnect the negative terminal of the battery. Safety first.

  1. Locate and Remove the Relay: Identify the relay securely in slot 8 of the under-hood power distribution box. Carefully pull it straight out of its socket. Inspect the relay body and its terminals for obvious signs of burning, melting, or corrosion. Any physical damage warrants replacement immediately.
  2. Understand the Relay Pinout: Looking at the bottom of the relay, you'll see four or five metal prongs (terminals). Standard Bosch-style relays use these terminal designations:
    • Terminal 85: Coil ground (controlled by PCM).
    • Terminal 86: Coil power (comes from a fused ignition source).
    • Terminal 87: Power OUT to the fuel pump circuit.
    • Terminal 30: Constant fused battery power IN.
    • (Some 5-pin relays have an additional Terminal 87a, normally unused for the fuel pump application).
    • Note: Consult your Ranger's specific relay socket and diagram if possible, but the layout is usually standard.
  3. Bench Testing with Multimeter:
    • Continuity Check:
      • Set your multimeter to measure resistance (ohms Ω).
      • Probe the relay pins corresponding to the coil circuit: Terminal 85 and Terminal 86. You should measure resistance (typically between 50 and 150 ohms). A reading of 0 ohms (dead short) or infinite Ohms/L (open circuit) means the coil is bad – replace the relay.
      • Probe the relay pins corresponding to the normally OPEN switch contacts: Terminal 30 and Terminal 87. The meter should read infinite Ohms/L (indicating the contacts are open).
    • Coil Energization Test:
      • Find a small 9V or 12V battery (like a motorcycle battery or even a fresh PP3 9V battery in a pinch).
      • Connect the positive side to Terminal 86 and the negative side to Terminal 85. You should hear and feel a distinct click as the relay coil activates.
      • While keeping the coil energized, probe Terminal 30 and Terminal 87 again with your meter set to continuity or resistance. It should now read 0 ohms (or very low resistance), indicating the contacts closed successfully. If you don't get this continuity when energized, the internal contacts are burned or stuck – replace the relay.
  4. In-Vehicle Circuit Testing:
    • Power Check: Reconnect the negative battery cable temporarily. Turn the ignition to the "Run" position (do not crank). Set your multimeter to measure DC Volts (20V scale). Carefully probe the Terminal 30 slot in the empty relay socket. It should read full battery voltage (approx. 12.6V).
    • Ground Control Check: Keep the multimeter in DC Volts. With the ignition still in "Run", probe the Terminal 85 socket. The PCM should be providing a ground signal here for 1-2 seconds. The multimeter should show close to zero volts when this signal is active. If you have power at Terminal 30 but no ground signal at Terminal 85 (voltage stays high, around 12V), the issue lies with the PCM or its circuit control path, not the relay.
    • Pump Power Output Simulation (Jumper Wire Test - USE CAUTION): This test directly activates the fuel pump circuit. IMPORTANT: Ensure the key is in the "OFF" position before this step. Connect one end of your jumper wire to the Terminal 30 socket (which has constant battery voltage). Connect the other end briefly to the Terminal 87 socket in the relay box. You should hear the fuel pump immediately start running in the tank. If you hear the pump run with the jumper wire, it confirms power delivery through the circuit and that the pump itself works, strongly indicating the relay was the problem. If you do NOT hear the pump run:
      • Double-check you used the correct sockets.
      • Verify the fuel pump fuse is intact (see fuse section below).
      • Suspect issues like the fuel pump itself, wiring harness damage, or the inertia switch being tripped.
  5. Socket Test: Before condemning the relay or hunting for other issues, while the relay is removed, inspect the relay socket. Look for any signs of burnt plastic, melted terminals, loose wires, or bent/broken pins within the connector. Try gently reseating the relay if intermittent issues are suspected. Corrosion can build up inside the socket terminals over time, preventing good contact.

Confirming the Health of the Fuse: An Essential Partner to the Relay

The fuel pump relay relies on good fuses. Two critical fuses reside near the relay:

  1. Fuse F1.8 (20A): This fuse protects the fuel pump circuit itself. It supplies the high current flowing from the relay (Terminal 87) to the fuel pump. If this fuse is blown, replacing the relay won't help – power never reaches the pump. Always pull fuse F1.8 and check its integrity visually. Look for a broken element inside the clear top. Replace it with an identical 20 Amp fuse if blown. Check it every time you suspect a relay or pump issue.
  2. Fuse F2.10 (7.5A or 10A - Consult Box Lid): This fuse protects the control side power for the relay coil (Terminal 86). This fuse provides the initial power needed to activate the relay coil when the key is turned. Locate and verify its condition using the lid diagram. Replace with the correct rating if blown.

A blown F1.8 fuse sometimes indicates a failing fuel pump drawing too much current, but it can also be caused by a wiring short.

Replacing the Fuel Pump Relay: A Quick Fix

Once diagnosed as faulty, replacing the relay in your 99 Ranger is straightforward:

  1. Obtain the Correct Replacement: The standard relay for a 99 Ranger fuel pump circuit is a Bosch-style ISO mini relay (often called a "Fogu" relay). You'll find cross-references like:
    • Ford Part Numbers: F5TZ-9345-AA, F57Z-14B192-AA (confirm fitment)
    • Bosch Part Number: 0 332 019 152
    • Commonly found brand equivalents: Standard Motor Products RY-191, ACDelco D1741, Motorcraft DY-198, Tridon TR-191.
    • Any automotive parts store will have this type of relay. Bring your old one to match physically if uncertain. Avoid the cheapest no-name brands – stick with reputable suppliers for durability.
  2. Installation: Ensure the ignition is OFF. Match the prong pattern of the new relay to the socket. Align it carefully and press it firmly and squarely into socket number 8 until it clicks and is fully seated. Do not force it. Confirm it sits at the same depth as the surrounding relays. Reconnect the battery negative terminal if it was disconnected.
  3. Post-Installation Check: Turn the ignition key to "Run." Listen carefully at the rear of the truck for the 1-2 second fuel pump hum. If you hear it, attempt to start the engine. It should start normally if the relay was the only issue.

Crucial Considerations Beyond the Relay

While the relay is a common failure point, a no-start condition can have other causes. If replacing the relay doesn't fix the problem:

  1. Fuel Pump Failure: The electric fuel pump inside the fuel tank can fail entirely. Diagnosed by confirming no power at the pump connector when commanded (using the jumper method at the relay socket is a strong initial test) or by testing fuel pressure directly at the fuel rail test port. Fuel pump replacement requires lowering the fuel tank and is significantly more involved.
  2. Fuel Pump Fuse F1.8: Did you confirm fuse F1.8 after replacing the relay? If replacing the relay triggered a blown fuse F1.8 immediately upon key-on, suspect a short circuit in the wiring downstream of the relay (towards the pump) or a dead-shorted fuel pump.
  3. Tripped Inertia Switch: The 99 Ranger has a fuel pump inertia safety switch, usually located on the passenger side interior firewall (behind the kick panel or under the glovebox area). This switch is designed to cut power to the fuel pump in the event of a collision. They can sometimes trip due to a severe bump or even accidentally kicked by a passenger. Locate it and press the reset button firmly.
  4. Fuel Pump Wiring Harness: Wiring damage between the relay socket and the fuel pump or from the relay to the PCM can cause power loss. Inspect for chafing, corrosion (especially near connectors), or rodent damage. Use a wiring diagram to perform voltage drop tests on critical wires if necessary.
  5. PCM Malfunction: A failure in the PCM preventing it from sending the ground signal to the relay coil (Terminal 85) will prevent relay activation. Testing for the ground signal at socket Terminal 85 is essential before assuming the PCM is bad. This is less common than relay failure itself but possible.
  6. Bad Grounds: Ensure the fuel pump has a good chassis ground, and that the PCM itself has good grounds. Corroded or loose ground points can disrupt circuit operation. Inspect and clean ground connections relevant to the fuel injection system. The wiring diagram will show ground locations.
  7. Fuel Tank Issues: Extremely low fuel level (below what the gauge shows), a completely plugged fuel filter (rare, but the filter is on these trucks), or significant water contamination can mimic pump or relay issues, though usually with different symptoms than complete silence from the pump. Check fuel level first.

Preventing Future Fuel Pump Relay Problems

While failures can be unpredictable, a few proactive steps help:

  • Use Quality Replacement Relays: Stick with Motorcraft, Bosch, Standard Motor Products, or other reputable brands. Cheap generic relays may work initially but are prone to premature internal contact failure.
  • Maintain Electrical Connections: When working under the hood, occasionally check the relay socket and fuse contacts for signs of corrosion. A light coating of dielectric grease in the sockets can help prevent future corrosion, improving connection reliability.
  • Address Wiring Problems Promptly: If you notice any damaged wiring harnesses in the engine compartment, repair them correctly to prevent shorts or ground issues that could stress the relay or fuses. Cover exposed wires immediately.
  • Avoid Overloading Circuits: Adding high-power aftermarket accessories tapped into the fuel pump relay circuit or nearby fuses is a bad practice that can overload the relay or fuse, leading to failure or fire risk. Use dedicated circuits with appropriate relays for auxiliary equipment.
  • Know Where it Is: Familiarity with the relay location saves crucial time when a no-start situation arises, especially away from home. Keep the fuse box diagram accessible.

Addressing Common Concerns (FAQ)

  • "Can I drive my 99 Ranger with a bad fuel pump relay?"
    No. If the relay is completely failed, the fuel pump gets no power, meaning no fuel reaches the engine. The truck will not run at all. An intermittently failing relay might cause unexpected stalling while driving, which is extremely dangerous. Replace it immediately.
  • "Can I jump the relay to get home?"
    Temporarily, yes – but only if absolutely necessary and with extreme caution. Using a heavy-gauge fused jumper wire to connect the Terminal 30 socket directly to the Terminal 87 socket in the relay box will force the fuel pump to run continuously as long as the key is "On," bypassing the relay and PCM control. This is an emergency measure only. Significant Risks:
    • The fuel pump runs non-stop with the key on, draining the battery if the truck isn't running.
    • It bypasses the important automatic shutdown triggered by the inertia switch in a collision, increasing fire risk.
    • It can blow the fuel pump fuse if there's a wiring problem the bypass wire itself isn't fused.
    • It prevents the PCM from using the "Clear Flood Mode" strategy if needed.
    • Only do this to move the vehicle a very short distance to a safe location for permanent repair. Remove the jumper immediately after. Use a fused jumper if possible (e.g., fuse holder inline).
  • "Why is tapping the relay a temporary fix?"
    Internal contacts inside the relay can become pitted, corroded, or stuck open due to arcing over time. Physically tapping the relay housing might jar the contacts enough to momentarily bridge the gap, allowing the pump to get power. This is a clear sign the relay contacts are worn out, and the relay requires replacement soon. It is not a permanent solution.
  • "Are relays generic?"
    The form factor (size and pin configuration) for the 99 Ranger fuel pump relay is a standard Bosch ISO mini relay. Functionally, this type is very common. However, the electrical rating matters. Ensure any replacement relay you use matches or exceeds the electrical ratings printed on the original relay or specified by Ford (typically rated for switching at least 20-30 amps). Using a relay rated for significantly less current could cause it to fail prematurely or not handle the pump load safely.
  • "How long does a fuel pump relay last?"
    There's no set lifespan. Original relays often last 10-15 years or more. Aftermarket quality relays should also be durable. Extreme heat cycles under the hood and electrical arcing eventually take a toll. Having one fail is often just bad luck. Keep a spare relay in your glove box – they are inexpensive and compact.
  • "Is the PCM power relay the same as the fuel pump relay?"
    No. While physically identical and located in the same under-hood power box, they serve different circuits. Swapping them to test can work, only if the truck starts normally afterward. If it doesn't start after swapping, it doesn't conclusively prove the fuel pump relay is bad – the PCM relay might have been bad too. If it does start after swapping, it strongly indicates the original fuel pump relay was faulty, and both should be replaced. Do not leave relays swapped long-term. Always return them to their designated sockets after testing.

When Professional Help is Needed

If you've replaced the relay and verified the fuse F1.8, performed the jumper wire test successfully (heard the pump run), but the truck still won't start, the problem lies elsewhere in the fuel or ignition system. Similarly, if the initial jumper wire test at the relay socket fails to activate the pump (and fuses are good), diagnosing becomes more complex. This is the time to seek a qualified automotive technician. They possess specialized diagnostic scanners, fuel pressure gauges, wiring diagrams, and experience to efficiently pinpoint the root cause, whether it's a deeper electrical wiring fault, a failed pump, a sensor issue, or engine mechanical problems. Don't keep throwing parts at the problem without solid evidence.

Back to blog