1990 Ford Bronco Fuel Pump Relay Location: The Complete Guide to Finding, Testing, and Replacing It
If you own a 1990 Ford Bronco and your fuel pump won't shut off or the engine won't start, the fuel pump relay is the first thing you should check. The relay is located in the power distribution box under the hood, on the driver's side near the firewall. This box is also called the fuse box or relay box. The fuel pump relay is a small, square, black component that plugs into the box. It controls power to the fuel pump. When the relay fails, it can cause the pump to run continuously, not run at all, or cause starting issues.
Understanding where this relay is and how to test it can save you hours of frustration and hundreds of dollars in unnecessary repairs. This guide walks you through everything you need to know, from locating the relay to diagnosing problems and replacing it.
Where Is the Fuel Pump Relay on a 1990 Ford Bronco?
The 1990 Ford Bronco has its fuel pump relay inside the Power Distribution Box (also called the fuse/relay box). This box is located under the hood, mounted on the driver's side fender, near the firewall.
To find it:
- Open the hood and look toward the back of the engine bay on the driver's side. You will see a black plastic box with a removable lid.
- Remove the lid by pressing the tabs on the sides. On the inside of the lid, there is usually a diagram showing which fuse or relay is which.
- Look for the relay labeled "Fuel Pump" or "FP." It is a square, black relay, typically one of the larger relays in the box. It is not the same as the EEC power relay or the horn relay, though they look similar.
If the diagram on the lid is missing or faded, the fuel pump relay is usually the relay that is closest to the fender, in the middle row of the box. The relay directly controls the electric fuel pump located inside the fuel tank.
What Does the Fuel Pump Relay Do?
The fuel pump relay is an electrical switch. When you turn the ignition key to the "ON" position, the relay closes and sends power to the fuel pump. The pump then pressurizes the fuel system. The relay is designed to only stay on for a few seconds if the engine does not start, to prevent the pump from running with no oil pressure. Once the engine runs, the relay stays closed, keeping the pump running.
If the relay sticks closed, the fuel pump will run continuously, even with the key off. This can drain the battery and cause the pump to overheat. If the relay fails open, the pump will not get power, and the engine will not start.
Common Symptoms of a Bad Fuel Pump Relay
Knowing the symptoms of a bad fuel pump relay can help you diagnose the problem quickly. Here are the most common signs:
1. Fuel Pump Runs Continuously – Even after you turn off the ignition, you can hear the fuel pump buzzing from the rear of the vehicle. This is a clear sign the relay is stuck closed.
2. Engine Cranks But Won't Start – If the relay fails to close, the pump gets no power. You will hear the starter turning the engine over, but it will not fire. This is the most common symptom of a failed relay.
3. No Sound from the Fuel Pump – When you turn the key to the "ON" position, you should hear a brief hum from the fuel pump for about 2 seconds. If you hear nothing, the relay or the pump itself may be dead. Check the relay first.
4. Intermittent Starting – Sometimes the truck starts fine, other times it won't. This can happen when the relay contacts are worn and only sometimes make connection.
5. Stalling While Driving – If the relay loses connection while you are driving, the engine will stall and may not restart until the relay cools down or is tapped.
How to Test the Fuel Pump Relay
Testing the fuel pump relay is simple and requires only a few tools. You can do it without removing the relay from the box, but for a thorough test, pull it out.
Tools Needed:
- 12-volt test light or multimeter
- Small flathead screwdriver (to pry the relay out)
- Jumper wire (optional)
Step 1: Locate the relay in the power distribution box. Mark its position so you do not mix it up with other relays.
Step 2: Visual inspection. Look at the relay for any signs of melting, cracks, or corrosion on the terminals. If it looks damaged, replace it.
Step 3: Listen for the click. Have a helper turn the ignition key to the "ON" position. You should hear an audible click from the relay box. If you hear the click, the relay coil is likely working. If no click, the relay is bad or not getting power from the ignition.
Step 4: Test for power at the relay. Use a test light. Ground the clip and probe the terminal that is labeled "power from battery." With the key off, you should have power here. If not, check the fuses. Then turn the key to "ON" and probe the terminal that controls the relay coil. The test light should light up briefly (about 2 seconds) then go out.
Step 5: Test the relay output. With the key on, probe the terminal that leads to the fuel pump. The light should light up for 2 seconds. If it does, the relay is passing power. If it does not, the relay is bad.
How to Replace the Fuel Pump Relay
Replacing the fuel pump relay is one of the easiest repairs on a 1990 Bronco. You can do it in under 5 minutes.
1. Remove the old relay. Using a small flathead screwdriver, gently pry the relay straight up out of its socket. Do not twist it. It should come out with moderate effort.
2. Inspect the socket. Look inside the socket for any corrosion, melted plastic, or debris. If the socket is damaged, you may need to replace the entire power distribution box, but usually, it is fine.
3. Install the new relay. Push the new relay straight down into the same socket. It should click into place. Make sure it is fully seated.
4. Test the system. Turn the ignition key to the "ON" position. You should hear the fuel pump prime for 2 seconds. Start the engine. If everything works, the repair is done.
Important: Use a relay that matches the original specifications. Do not use a generic automotive relay unless it is rated for the same amperage. The correct relay for a 1990 Ford Bronco is typically a standard 30-amp relay.
Why Your Fuel Pump May Still Not Work After Replacing the Relay
If you replace the fuel pump relay and the pump still does not work, the problem lies elsewhere. Here are other common causes:
1. Blown fuse. The fuel pump circuit has a fuse in the same power distribution box. Check the fuse labeled "Fuel Pump" or "FP." If it is blown, replace it with the same amperage.
2. Bad fuel pump. The pump itself may be dead. On a 1990 Bronco, the fuel pump is inside the fuel tank. To test it, you can apply 12 volts directly to the pump connector at the tank. If it does not run, the pump needs replacement.
3. Faulty inertia switch. The 1990 Bronco has an inertia switch that cuts power to the fuel pump in a crash. It is located behind the kick panel on the passenger side floor. If this switch is tripped, the pump will not run. Press the reset button on top of the switch.
4. Wiring issues. Corroded or broken wires between the relay and the pump can cause no power. Check the wiring harness along the frame rail for damage.
5. Bad ground. The fuel pump needs a good ground connection. If the ground wire at the tank is loose or rusty, the pump will not work properly.
Where to Buy a High-Quality Fuel Pump for Your 1990 Ford Bronco
If you have tested the relay, fuses, and inertia switch, and the fuel pump is still not working, the pump itself is likely the problem. The original pump on a 1990 Bronco is over 30 years old, and even if it still runs, it may be weak or failing. Replacing it with a high-performance, reliable unit is the best way to get your truck back on the road.
KEMSO is a trusted brand that specializes in aftermarket fuel pumps. Their products are designed as direct OEM replacements, meaning they fit perfectly into your 1990 Bronco without any modifications. You do not need to cut wires or adapt brackets. Simply remove the old pump and install the KEMSO unit.
Here is why KEMSO fuel pumps are a great choice for your Bronco:
- High Performance: KEMSO pumps deliver consistent fuel pressure and flow, ensuring your engine runs smoothly under all conditions, whether you are driving on the highway or off-road.
- OEM Replacement: They are built to the exact specifications of the original pump. No guesswork, no hassle.
- Lifetime Warranty: KEMSO stands behind their products. Every pump comes with a lifetime warranty, giving you peace of mind that your investment is protected.
If you need a new fuel pump for your 1990 Ford Bronco, visit the KEMSO website to find the correct pump for your vehicle. Their customer service team can help you verify fitment. Browse their full selection of high-quality fuel pumps and accessories.
Click here to visit KEMSO and find the right fuel pump for your Bronco: https://www.kemsoracing.com/
Final Thoughts
The fuel pump relay on a 1990 Ford Bronco is located in the power distribution box under the hood, on the driver's side. It is a simple, inexpensive part that can cause major headaches if it fails. Before you spend money on a new fuel pump, always test the relay first. It takes less than 10 minutes and can save you from pulling the fuel tank.
If you do need to replace the fuel pump, choose a high-quality option like KEMSO to ensure longevity and reliability. A properly working fuel system is essential for a truck that has been on the road for over three decades. Keep your Bronco running strong by addressing fuel system issues promptly.
For more information on fuel pumps, diagnostics, and replacement guides, check out the KEMSO blog and product pages at https://www.kemsoracing.com/. They have detailed guides for many vehicles, including the 1990 Ford Bronco.