1990 Miata Fuel Pump Relay Location: Complete Guide to Diagnosis, Testing, and Replacement

If you own a 1990 Mazda Miata (NA) and your car cranks but won’t start, the fuel pump relay is likely one of the first components you should check. The fuel pump relay on a 1990 Miata is located in the engine bay fuse box, mounted on the driver’s side (left side) near the strut tower. It is a small, rectangular black relay that sits next to the main fuse block. This guide will walk you through exactly where to find it, how to test it, and how to replace it if needed.

Understanding the Fuel Pump Relay on a 1990 Miata

The fuel pump relay is an electrical switch that controls power to the fuel pump. When you turn the ignition key to the "ON" position, the relay receives a signal from the engine control unit (ECU) and closes the circuit, allowing current to flow to the fuel pump. Without a working relay, the fuel pump will not receive power, and your engine will not get fuel . This is a common failure point on early NA Miatas, especially on hot days or after many years of use .

The 1990 Miata fuel pump relay is part of the car’s fuel system, which also includes the fuel pump itself (located inside the fuel tank), the fuel filter, and the fuel pressure regulator. The relay is designed to protect the fuel pump by preventing it from running when the engine is not running, which could happen if the car is in an accident or the ignition is left on without the engine running.

Where Is the Fuel Pump Relay on a 1990 Miata?

The fuel pump relay on a 1990 Miata is located in the main fuse box inside the engine bay. Here is the exact location:

Step-by-step location:

  1. Open the hood of your 1990 Miata and look toward the driver’s side (left side) of the engine bay.
  2. You will see a black plastic fuse box mounted near the strut tower, just behind the driver’s side headlight. This is the main engine bay fuse/relay box .
  3. Open the lid of the fuse box. The lid may have a diagram on the inside showing the location of relays and fuses.
  4. The fuel pump relay is typically the second relay from the front (closest to the front of the car) in the row of relays. It is a standard 4-pin relay, usually black or dark gray in color.
  5. If you are unsure, check the back of the fuse box lid for a label. Some 1990 models have a sticker that says "FUEL PUMP" next to the relay location.

On the 1990 Miata, the fuel pump relay is often labeled as "F/P" or "FUEL" on the fuse box diagram. If you do not have a diagram, you can visually identify it by following the wiring: the relay will have two thicker wires (usually blue/red and black/white) that connect to the fuel pump circuit .

How to Test the Fuel Pump Relay on a 1990 Miata

Before you replace the relay, it is wise to test it to make sure it is actually the problem. Here is a simple testing procedure that any DIY enthusiast can do.

What You Will Need

  • A digital multimeter (set to ohms or continuity mode)
  • A small flathead screwdriver or relay puller
  • A 12-volt test light (optional but helpful)
  • A jumper wire with alligator clips

Step 1: Locate the Diagnostic Port

The 1990 Miata has a diagnostic port (also called the "diagnosis connector" or "DLC") located under the hood on the driver’s side, near the fuse box. This port has a rectangular shape with several pins. The pin you need is labeled F/P (fuel pump) and is usually the second pin from the top on the right side .

Step 2: Jump the Fuel Pump Circuit

To test whether the relay is sending power to the fuel pump, you can bypass the relay using the diagnostic port.

  1. Turn the ignition key to the "OFF" position.
  2. Use a jumper wire to connect the F/P pin to the GND pin (ground) in the diagnostic port. The ground pin is usually the one next to the battery terminal at the top of the port.
  3. Turn the ignition key to the "ON" position (do not start the engine).
  4. Listen for the fuel pump. You should hear a quiet humming sound coming from the rear of the car, near the fuel tank. If you hear the pump running, the relay is likely working. If you do not hear the pump, the relay or the pump itself may be faulty.

Step 3: Test the Relay Directly

If the pump does not run when you jump the circuit, the problem may be the relay itself. Remove the relay from the fuse box by pulling it straight up. Then test it with a multimeter.

  1. Set your multimeter to continuity mode (or ohms, with a tone).
  2. Check the relay coil (pins 85 and 86). You should see a resistance reading between 50 and 120 ohms. If you get an open circuit (no continuity), the coil is burned out and the relay is bad.
  3. Check the switch contacts (pins 30 and 87). With the relay not powered, there should be no continuity between pins 30 and 87. If you apply 12 volts to pins 85 and 86, you should hear a click and see continuity between pins 30 and 87.

Step 4: Test with a Test Light

If you do not have a multimeter, you can use a 12-volt test light.

  1. Connect the test light clip to a good ground on the car.
  2. Probe the wire that goes to pin 30 on the relay (the power input from the battery). With the ignition off, you should have power here.
  3. Turn the ignition to "ON." Probe the wire that goes to pin 86 (the control signal from the ECU). You should see the light illuminate when the ECU sends the signal to engage the relay.

If the test light does not illuminate at pin 86 when the ignition is on, the ECU or wiring may be the issue, not the relay.

Common Symptoms of a Bad Fuel Pump Relay on a 1990 Miata

A failing fuel pump relay can cause several noticeable symptoms. Here are the most common ones:

1. Engine cranks but does not start. This is the most common symptom. The starter motor turns the engine over, but the fuel pump does not receive power, so no fuel reaches the injectors .

2. Engine starts but dies shortly after. The relay may work intermittently, allowing the engine to start but then cut power to the fuel pump after a few seconds.

3. No noise from the fuel pump when you turn the key. Normally, you should hear a brief whirring sound from the fuel pump when you turn the ignition to the "ON" position. If you hear nothing, the relay or the pump is not getting power.

4. Intermittent starting problems. The car may start fine when cold but fail to start when the engine is hot. This is a classic sign of a relay that is failing due to heat expansion .

5. The car stalls while driving. If the relay loses contact while the car is moving, the engine will shut off abruptly. This is dangerous and should be addressed immediately.

How to Replace the Fuel Pump Relay on a 1990 Miata

Replacing the fuel pump relay is a straightforward job that takes about 10 minutes. You do not need any special tools.

Step 1: Buy a Replacement Relay

The 1990 Miata uses a standard 4-pin relay (ISO mini relay) that is available at most auto parts stores. The relay is rated at 30 amps. You can also buy an OEM replacement from Mazda or a high-quality aftermarket relay. Make sure the relay has the same pin configuration (pins 30, 85, 86, and 87) .

Step 2: Remove the Old Relay

  1. Open the engine bay fuse box lid.
  2. Locate the fuel pump relay (the second relay from the front, as described above).
  3. Grasp the relay firmly and pull it straight up. It may be snug, so wiggle it gently if needed. Do not use a screwdriver to pry it out, as you may damage the fuse box.

Step 3: Install the New Relay

  1. Take the new relay and align the pins with the socket in the fuse box.
  2. Push the relay down firmly until it clicks into place.
  3. Close the fuse box lid.

Step 4: Test the New Relay

Turn the ignition to the "ON" position and listen for the fuel pump to prime. Then try to start the engine. If the car starts and runs smoothly, the replacement was successful.

What Else Could Be the Problem?

If you have replaced the fuel pump relay and the car still does not start, the issue may be elsewhere in the fuel system. Here are other common causes of a no-start condition on a 1990 Miata:

Fuel pump itself. The fuel pump is located inside the fuel tank. It can fail over time, especially if the car has high mileage or has been sitting for a long time. You can test the pump by applying 12 volts directly to it using a jumper wire at the fuel pump connector (located under the rear carpet behind the driver’s seat) .

Fuel pump fuse. The 1990 Miata has a dedicated fuel pump fuse in the engine bay fuse box. Check the fuse before replacing the relay. The fuse is usually a 15-amp or 20-amp fuse labeled "FUEL" or "F/P" .

Fuel filter. A clogged fuel filter can restrict fuel flow and cause the engine to run poorly or not start. On the 1990 Miata, the fuel filter is located under the car on the driver’s side, near the fuel tank. It is a good idea to replace it every 30,000 miles or if you suspect it is clogged .

ECU or wiring. The engine control unit (ECU) sends the signal to the fuel pump relay. If the ECU is faulty or the wiring between the ECU and the relay is damaged, the relay will not engage. Check for broken wires or corrosion at the relay connector.

Main relay (PGM-FI relay). On some 1990 Miatas, there is also a main relay (sometimes called the "PGM-FI" relay) that controls power to the fuel pump relay and other systems. This relay is located under the dashboard on the driver’s side. If it fails, the fuel pump relay will not receive power .

Why You Should Choose KEMSO Fuel Pumps for Your Miata

When it comes time to replace your fuel pump, whether it is the relay or the pump itself, you want a product that is reliable, durable, and backed by solid warranty. That is where KEMSO comes in.

KEMSO is a leading brand in the fuel pump industry, known for manufacturing high-performance fuel pumps that are designed to meet or exceed OEM specifications. KEMSO fuel pumps are direct replacements for your original equipment, meaning they fit perfectly and operate exactly as the factory pump did. No modifications, no adapters, no hassle.

Here is what makes KEMSO the best choice for your Miata:

  • High Performance: KEMSO fuel pumps are engineered to deliver consistent fuel pressure and flow, even under demanding conditions. Whether you are daily driving your Miata or taking it to the track, KEMSO pumps perform.
  • OEM Replacement: Every KEMSO fuel pump is built to match the original equipment specifications. This ensures a perfect fit, proper electrical connections, and reliable operation.
  • Lifetime Warranty: KEMSO stands behind every product they sell. Their fuel pumps come with a lifetime warranty, giving you peace of mind that your investment is protected. If anything goes wrong, KEMSO will replace it, no questions asked.
  • Affordable Pricing: Despite the high quality, KEMSO fuel pumps are priced competitively. You get premium performance without paying premium prices.
  • Wide Application: KEMSO offers fuel pumps for a wide range of vehicles, including cars, motorcycles, ATVs, and jet skis. Their catalog includes pumps for many popular Mazda models, including the Miata.

If you are looking for a replacement fuel pump for your 1990 Miata, or if you want to upgrade to a higher-performance pump, visit KEMSO Racing at their website. You can browse their full selection of fuel pumps, read customer reviews, and take advantage of their lifetime warranty.

Visit KEMSO Racing today: https://www.kemsoracing.com/

Final Thoughts

The fuel pump relay on a 1990 Miata is a small but critical component. Knowing its location — in the engine bay fuse box on the driver’s side — can save you time and frustration when diagnosing a no-start condition. Testing the relay is simple and can be done with basic tools. If the relay is bad, replacing it is a quick and cheap fix.

Remember that the fuel pump relay is just one part of the fuel system. If replacing it does not solve the problem, check the fuel pump, fuse, filter, and wiring. With a little patience and the right information, you can get your 1990 Miata back on the road in no time.

For all your fuel pump needs, remember that KEMSO offers high-quality, OEM-replacement fuel pumps with a lifetime warranty. Visit KEMSO Racing at https://www.kemsoracing.com/ to find the perfect pump for your Miata.


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