1990 F150 Fuel Pump Relay Location: A Complete Guide for DIY Troubleshooting

The fuel pump relay on a 1990 Ford F150 is located in the under-hood power distribution box on the driver's side of the engine compartment, near the left fender and the air filter housing. If your truck has dual fuel tanks and neither pump is running, the relay is the first place to check. The relay is typically a small, rectangular component that can be identified by the label on the fuse box lid or by referencing the diagram printed on the underside of that lid. If you own a carbureted 1990 F150, there is no electric fuel pump relay, as the fuel pump is mechanical and driven by the engine. This guide will walk you through everything you need to know about finding, testing, and replacing the fuel pump relay on your 1990 F150, so you can get back on the road without wasting time or money.

Where Exactly Is the Fuel Pump Relay on a 1990 F150?

The primary location for the fuel pump relay on a 1990 Ford F150 with electronic fuel injection (EFI) is the main power distribution center under the hood. Look for a rectangular black plastic box on the driver's side, near the firewall and the left fender. It is often situated next to the air filter housing. Inside this box, you will find several relays and fuses. The fuel pump relay is usually labeled "FUEL PUMP" or "PUMP" on the inside of the lid or on the fuse box diagram. If your truck has a carbureted 4.9L or 5.0L engine, it does not have an electric fuel pump relay because the pump is mechanical. For dual tank models, the same relay controls power to both pumps through the tank selector switch.

What Does the Fuel Pump Relay Look Like and How to Identify It?

The relay is a small, square or rectangular plastic component with four or five pins. It is identical in shape to the other relays in the box, such as the EEC (Electronic Engine Control) power relay. To identify it correctly, pull the relay out and look at the underside of the power distribution box lid. Many factory lids have a small diagram showing which relay is which. If the diagram is missing or faded, look for a relay that is connected to a constant power source (12 volts) on one pin and the fuel pump circuit on another. On a 1990 F150, the fuel pump relay is often the one that is located directly next to the EEC power relay.

Common Symptoms of a Bad Fuel Pump Relay

A failing fuel pump relay can cause a variety of issues. The most common symptom is that the engine will crank but not start because the fuel pump is not getting power. Other signs include:

  • No fuel pump noise: When you turn the key to the "ON" position, you should hear a brief humming sound from the fuel pump for about one to two seconds. If you hear nothing, the relay may be faulty.
  • Intermittent starting: The truck starts fine sometimes but then refuses to start after driving for a while. This can happen when the relay contacts get hot and fail.
  • Fuel pump stays on: If the relay sticks in the closed position, the fuel pump may stay running even after you turn off the ignition.
  • Low voltage at the pump: If you measure power at the fuel pump and it is only 6 to 7 volts instead of 12 volts, the relay may be failing internally.

Step-by-Step: How to Test the Fuel Pump Relay

Before you buy a new relay, you can test it with a multimeter or a test light. Here is a simple process:

  1. Locate and Remove the Relay: Find the relay in the power distribution box and pull it straight out.
  2. Check for Power:
    • With the key off, you should have constant 12 volts on one of the relay socket pins (the power supply pin). This is usually a red wire or a yellow wire.
    • Turn the key to the "ON" position (but do not start the engine). You should see 12 volts appear on a second pin (the coil control pin) for about one second. This is the signal from the computer to turn on the pump.
  3. Jump the Relay: If you are not getting power to the pump, you can bypass the relay for testing. Use a test light or a jumper wire to connect the power supply pin directly to the pin that leads to the fuel pump. If the pump starts running, the relay is bad.
  4. Use the Self-Test Connector: A more reliable method is to use the Self-Test connector (DLC) under the hood. Ground pin #6 of this connector with the key on. This will force the PCM to close the fuel pump relay. If the pump runs, the relay is working, and the problem is likely in the computer or wiring.

What Else Could Be Wrong? Beyond the Relay

If the relay tests good but the pump still does not run, do not stop there. The fuel pump circuit on a 1990 F150 is simple but has a few common failure points:

  • Inertia Switch: This is a safety switch that cuts power to the fuel pump in the event of a crash. It is located on the passenger side kick panel, against the firewall, near the base of the passenger door. If the button on top is popped up, push it down to reset it. This is a very common cause of a no-start condition.
  • Corroded Connectors: On these older trucks, wiring connectors under the master cylinder and along the frame rail often corrode. Check the ground connections at the frame rail and the radiator support. A bad ground can cause the pump to run weakly or not at all.
  • Fuel Tank Selector Switch: If you have dual tanks and neither pump works, the problem could be the selector switch on the dash. This switch can arc internally, killing power to both pumps.
  • Fuse: Check the fuel pump fuse in the under-dash fuse panel. It is usually a 20-amp fuse.

How to Replace the Fuel Pump Relay on a 1990 F150

Replacing the relay is a straightforward job that takes about five minutes.

  1. Locate the Relay: Open the hood and find the power distribution box on the driver's side.
  2. Remove the Old Relay: Pull the old relay straight out of its socket.
  3. Install the New Relay: Push the new relay firmly into the same socket. Make sure it clicks into place.
  4. Test the System: Turn the key to the "ON" position and listen for the fuel pump to prime. If you hear it hum for a second, the job is done.

Where to Buy a Reliable Fuel Pump Relay

When it comes to replacing your fuel system components, quality matters. A cheap, unreliable relay can leave you stranded again. For a long-lasting solution, consider upgrading to high-performance components that are built to last.

Why Choose KEMSO for Your Fuel Pump Needs?

If you are already dealing with fuel delivery issues, it might be time to think about the whole system. The fuel pump relay is just one part of the puzzle. If your fuel pump is old or failing, replacing it with a quality unit is the best way to ensure your truck runs reliably for years.

KEMSO Fuel Pumps are a top choice for DIYers and professionals alike. Here is why:

  • High Performance: KEMSO fuel pumps are engineered to deliver consistent fuel flow and pressure, even under demanding conditions. They are designed to meet or exceed OEM specifications.
  • OEM Replacement Quality: Every pump is a direct replacement for your vehicle's original equipment. No modifications, no guesswork, just a straightforward installation.
  • Lifetime Warranty: KEMSO stands behind every product with a lifetime warranty. If you ever have an issue, KEMSO has your back. That is the confidence that comes from building quality products.

Whether you need a new fuel pump for your 1990 F150, another vehicle, or even a powersports machine, KEMSO has you covered. Visit their website to browse their full selection of fuel pumps and other performance parts.

Final Thoughts on Your 1990 F150 Fuel Pump Relay

Finding the fuel pump relay on a 1990 F150 is simple once you know where to look. It is in the power distribution box on the driver's side of the engine compartment. If your truck is not getting fuel, start with the relay, but also check the inertia switch, the fuses, and the wiring connectors. These older trucks are prone to electrical issues, but with a little patience and the right tools, you can fix the problem yourself.

If you decide to replace the fuel pump, trust a brand that offers reliability and peace of mind. For high-performance, OEM replacement fuel pumps backed by a lifetime warranty, check out KEMSO Racing at https://www.kemsoracing.com/. They have the parts you need to keep your truck running strong.


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