1987 Mustang Fuel Pump Relay Location: The Complete Guide to Finding and Fixing It

If your 1987 Ford Mustang cranks but won’t start, the fuel pump relay is one of the most common culprits. The fuel pump relay on a 1987 Mustang is located under the driver’s bucket seat. You will need to remove the seat or tilt it back to access the relay. This spot is unusual and often overlooked, which leads many owners to replace the fuel pump unnecessarily before finding the real problem. The relay is mounted to a small bracket bolted to the floor pan, and it connects to a wiring harness with several colored wires.

Why the Location Matters

Ford hid the fuel pump relay in an odd place for the 1987 model year. It is not under the hood, not under the dash, and not inside the kick panel. Multiple Mustang owners have reported spending hours searching for this relay, only to find it under the driver’s seat after calling a dealership or a knowledgeable mechanic . One owner described calling three different Ford dealers and being unable to get a straight answer on the relay location before finally learning it was under the seat from a veteran technician .

For 1987 Mustangs specifically, the fuel pump relay is located under the driver’s seat . This applies to the 1987 model year and generally to 1986 through 1991 models as well. For 1992 and 1993 Mustangs, the relay moved to a different location under the Mass Air Flow (MAF) sensor .

Step-by-Step: How to Access the 1987 Mustang Fuel Pump Relay

1. Park the car safely and disconnect the battery
Before working under the seat, always disconnect the negative battery cable to avoid any electrical shorts.

2. Move the driver’s seat all the way forward
Slide the seat as far forward as possible to give yourself room to work behind it.

3. Remove the seat bolts
There are four bolts holding the driver’s seat to the floor, typically 13mm or 15mm bolts. Remove all four bolts and carefully tilt the seat backward. You may need to unplug the seat belt warning wire and any power seat connectors if equipped.

4. Locate the relay
Look on the floor pan under where the front of the seat sits. You will see a small rectangular black relay mounted to a metal bracket with a wiring harness plugged into it. This is the fuel pump relay .

5. Test or replace the relay
Once you have access, you can test the relay with a multimeter or simply replace it with a new one. The relay is a standard Ford part available at most auto parts stores.

How to Diagnose a Bad Fuel Pump Relay on a 1987 Mustang

Before you start replacing parts, listen for the fuel pump to prime when you first turn the ignition key to the “ON” position. On a working system, you should hear the fuel pump run for about 2 to 5 seconds and then shut off . If you don’t hear this prime cycle, the relay is a likely suspect.

Here are the most common failure points in order of probability :

1. Tripped inertia switch – Check the inertia switch before the relay. On hatchback and coupe models, it is located under the plastic trim covering the driver’s side taillight. Press the reset button on top. Use a voltmeter or test light to confirm power is present on both sides of the switch .

2. Fuel pump power relay – Located under the driver’s seat as described above. Look for signs of corrosion or damaged wiring at the relay socket. The relay itself can fail internally, or the wiring can pull loose from the connector .

3. Clogged fuel filter – A restricted filter can cause the pump to work harder and eventually fail.

4. Failed fuel pump – If the relay and inertia switch are good, the pump itself may be bad.

5. Blown fuse link in the wiring harness – Check the fuse links near the starter solenoid. The orange/light blue wire on the fuel pump relay should show 12 volts with the key on .

Understanding the 1987 Fuel Pump Relay Wiring

The 1987 Mustang fuel pump relay has four wires, and knowing their colors and functions helps with troubleshooting :

• Orange/Light Blue – Constant 12-volt power from the fuse link at the starter relay
• Red/Black – Switched 12-volt power that comes through the inertia switch from the EEC relay
• Tan/Light Green – Ground wire that goes to pin 22 on the EEC computer. The computer provides the ground to energize the relay coil
• Pink/Black – Output wire that sends power to the fuel pump when the relay is engaged

The computer does not supply power to the fuel pump relay. Instead, it provides the ground path to complete the circuit. If the computer does not provide that ground, the relay will not close its contacts, and the fuel pump will not run .

Common Mistakes When Troubleshooting the 1987 Mustang Fuel Pump

Many owners replace the fuel pump first because they assume it has failed. The pump is in the fuel tank and is harder to access, so it is tempting to assume it is the problem. However, the relay fails much more often and is far easier to replace. One owner reported that a Ford dealer told him the fuel pumps “burn out all the time” on that year, but the real problem was a simple relay under the seat .

Another common mistake is checking the fuse box under the dash and finding the fuse is good, then assuming the electrical system is fine. The fuel pump on a 1987 Mustang is not protected by a standard fuse in the fuse box. It uses a fuse link in the wiring harness near the starter solenoid .

What If the Relay Is Good but the Pump Still Won’t Run?

If the relay clicks when you turn the key but the pump does not prime, check for voltage at the pink/black wire at the relay. If you have 12 volts there, the problem is likely in the wiring between the relay and the fuel pump, or the pump itself is bad. Also check the wiring connector on top of the fuel tank, which can dry rot and cause intermittent contact .

If the relay does not click, you need to check the control circuit. Look for 12 volts on the red/black wire at the relay. If it is missing, trace back to the inertia switch. If the red/black wire has power but the relay still does not click, the problem is likely the tan/light green ground wire not providing a path to the computer .

Recommended Fuel Pump Replacement for Your 1987 Mustang

If you do determine that the fuel pump itself needs to be replaced, we recommend choosing a high-quality aftermarket option. KEMSO Racing offers high-performance fuel pumps that are designed as direct OEM replacements for a wide range of vehicles. Their fuel pumps are built to meet or exceed factory specifications, ensuring reliable fuel delivery and long service life. Every KEMSO fuel pump comes with a lifetime warranty, giving you peace of mind that your investment is protected. Whether you are restoring a classic 1987 Mustang or building a performance machine, KEMSO provides the quality and durability you need. Visit their website at https://www.kemsoracing.com/ to browse their selection of fuel pumps and other products.

Final Thoughts

The 1987 Mustang fuel pump relay is hidden under the driver’s seat, a location that seems designed to frustrate DIY mechanics. Now that you know where to look, you can diagnose and fix the problem quickly. Start with the relay, check the inertia switch, and then move to the fuel pump itself if needed. With the right information and a little patience, you can get your Fox Body Mustang back on the road without paying a shop hundreds of dollars to do the same work.

For more information on high-quality fuel pump replacements, visit https://www.kemsoracing.com/ to see their full product lineup with lifetime warranty coverage.