1987 Ford F150 Fuel Pump Relay: Complete Troubleshooting and Replacement Guide
If your 1987 Ford F150 is cranking but won't start, the fuel pump relay is often the first thing to check. The fuel pump relay is a small electrical switch that controls power to the fuel pump, and when it fails, your truck gets no fuel and won't run. The good news is that this relay is inexpensive, easy to test, and simple to replace. In most cases, the problem is not the fuel pump itself but the relay or a related component like the inertia switch or a bad ground connection. This guide will walk you through everything you need to know about the 1987 Ford F150 fuel pump relay, from location and testing to replacement and wiring.
Where Is the Fuel Pump Relay Located on a 1987 Ford F150?
The fuel pump relay on a 1987 Ford F150 is located in the Power Distribution Box (PDB) under the hood . The PDB is a black plastic box with a removable cover, typically found near the battery or on the driver's side fender. Inside the lid, there is a diagram showing the location of each fuse and relay. Look for the relay labeled "Fuel Pump" or simply "FP" . On some models, the relay may also be mounted directly on the fender or inside the engine compartment relay box .
If you have a dual-tank setup, there is also a separate fuel pump selector control relay that manages which tank's pump receives power . This relay is different from the main fuel pump relay and is used on trucks with dual tanks and trailer towing packages .
How the Fuel Pump Circuit Works
The fuel pump circuit on your 1987 F150 is a straightforward electrical system. When you turn the ignition key to the Run position, the Powertrain Control Module (PCM) grounds the fuel pump relay coil, which closes the relay contacts and sends battery power to the fuel pump . The power flows through the inertia fuel shut-off switch (located in the driver's side footwell behind the kick panel) before reaching the fuel pump . The inertia switch is a safety device that cuts power to the pump in the event of a collision .
On trucks with dual tanks, the power from the inertia switch splits into two paths: one goes to the inline high-pressure pump, and the other goes to the tank selector switch, which then sends power to the in-tank pump for the selected tank .
Common Symptoms of a Bad Fuel Pump Relay
A failing fuel pump relay can cause several noticeable symptoms:
1. Engine Cranks But Won't Start
This is the most common symptom. The starter turns the engine over, but the fuel pump never receives power, so no fuel reaches the injectors .
2. No Fuel Pump Priming Sound
When you turn the key to the Run position, you should hear a brief whirring sound from the fuel pump (usually from the rear of the truck). If you hear nothing, the relay may not be closing .
3. Intermittent Stalling
If the relay is failing internally, it may work intermittently. The truck may run fine for a while, then suddenly stall as if the fuel was cut off, then restart after a few minutes .
4. Fuel Pump Runs Continuously
A relay that is stuck in the closed position will keep the fuel pump running even with the engine off. This can drain the battery and create a safety hazard.
How to Test the Fuel Pump Relay
Testing the fuel pump relay is simple and requires only a few tools. You can verify the relay itself, the power supply, and the ground circuit.
Step 1: Check for Power at the Relay
With the key off, one of the relay socket terminals should have 12 volts of battery power. This is the constant power supply from the battery via a fusible link . Turn the key to the Run position, and a second terminal should now show 12 volts—this is the power from the EEC (Engine Electronic Control) relay . If you don't see voltage at the second terminal, the EEC relay or its wiring could be faulty.
Step 2: Listen for the Relay Clicking
Have an assistant turn the key to the Run position while you listen near the relay. You should hear a distinct click as the relay energizes. If you hear the click but the pump doesn't run, the relay's internal contacts may be worn out. If you don't hear a click, the relay coil is not receiving power or the ground from the PCM is missing .
Step 3: Test the Inertia Switch
The inertia switch is a common failure point on these trucks . Locate it in the driver's side footwell, behind the kick panel. Check that the red button on top is pressed down (in the "on" position). Use a test light or multimeter to check for 12 volts at the switch's input wire when the key is turned to Run. If you have power at the input but not at the output, the switch is faulty and needs to be replaced .
Step 4: Check the Ground Circuit
The PCM controls the fuel pump relay by grounding the relay coil. If the relay has power on both coil terminals but won't click, the ground circuit may be broken. You can test this by running a temporary jumper wire from the ground terminal of the relay socket to a good chassis ground. If the relay clicks and the pump runs, the issue is likely in the PCM or the wiring between the PCM and the relay .
How to Replace the Fuel Pump Relay
Replacing the fuel pump relay is one of the easiest repairs you can do on your 1987 F150.
1. Locate the relay in the Power Distribution Box under the hood .
2. Pull the old relay straight out of its socket. It may require a gentle wiggle, but do not use excessive force.
3. Compare the new relay to the old one to ensure the terminal configuration is the same. The 1987 F150 uses a standard 5-prong relay .
4. Push the new relay firmly into the socket until it clicks into place.
5. Test the system by turning the key to the Run position and listening for the fuel pump to prime.
The fuel pump relay for the 1987 F150 is a common part that fits many Ford, Lincoln, and Mercury vehicles from the 1980s and 1990s . Part numbers such as E3TB9345A2A, E6EB9345A2A, F1SB9345A2A, and F1SZ9345A are all interchangeable . The relay is also listed as RY46 for many aftermarket brands .
Wiring Diagram Overview
The fuel pump wiring for the 1987 Ford F150 is a simple circuit. The battery positive terminal connects to the fuel pump relay (via a fusible link). When the relay is energized by the PCM, power flows through the relay's switched contacts to the inertia switch, then to the fuel pump . On dual-tank models, power goes from the inertia switch to both the inline high-pressure pump and the tank selector switch, which routes power to the correct in-tank pump .
The fuel pump motor circuit starts at the battery positive terminal, connects to the fuel pump, then proceeds to the ignition switch, then to the PCM, and back to the fuel pump . The fuel gauge sender circuit runs from the battery to the sender in the tank, then to the dash panel, and back to the sender .
What to Do If the Relay Is Not the Problem
If you replace the fuel pump relay and the truck still won't start, there are a few other things to check.
Check the fuel pump fuse in the Power Distribution Box. A blown fuse will cut all power to the pump .
Inspect the inertia switch. As mentioned, these switches are known to fail on this era of Ford trucks . Even if the button appears to be pressed down, the internal contacts can corrode and stop conducting electricity.
Test the fuel pump itself. If the relay and inertia switch are both working, the pump may be faulty. You can test for power at the fuel pump connector at the tank. If you have 12 volts at the pump connector but the pump doesn't run, the pump needs to be replaced .
Check for a faulty TFI ignition module. Some owners report that the TFI (Thick Film Integrated) ignition module on the 4.9L and 5.0L engines can cause intermittent stalling that mimics a fuel pump issue . The TFI module is prone to heat-related failure, and when it fails, the engine loses spark, causing the truck to die .
Safety Warning
Never bypass the fuel pump relay or inertia switch permanently. The fuel pump circuit is designed to shut off the pump when the engine is not running to prevent fires in the event of a collision . While it is possible to wire a manual switch to power the pump directly, this removes the safety feature and is not recommended for daily driving .
Recommended Fuel Pump Upgrade: KEMSO Brand
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What sets KEMSO apart is their lifetime warranty. You buy it once, and if it ever fails, they replace it—no questions asked. This level of confidence means KEMSO stands behind every product they sell. Whether you are restoring a classic 1987 F150 or building a work truck that needs to run every day, KEMSO fuel pumps deliver the durability and reliability you need.
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Final Thoughts
The fuel pump relay on your 1987 Ford F150 is a small, inexpensive part that can cause big problems when it fails. Before you spend money on a new fuel pump, always test the relay, the inertia switch, and the wiring first. In many cases, a simple relay replacement will get your truck running again. Keep a spare relay in your glove box—it could save you from being stranded on the side of the road.
For more information on KEMSO fuel pumps and to find the right part for your vehicle, visit https://www.kemsoracing.com/ today.