1990 Chevy Fuel Pump Relay: Location, Testing, and How to Jump It

The 1990 Chevy fuel pump relay is a small but critical component that controls power to your fuel pump. If your truck cranks but won't start, a faulty relay is often the culprit. The relay is typically located in the under-hood fuse box on the firewall, and you can test it by listening for a click, swapping it with a similar relay, or jumping it with a wire. If the pump runs when jumped, simply replace the relay. If not, the issue may be the pump itself, wiring, or fuses.

This guide covers everything you need to know about the 1990 Chevy fuel pump relay—where to find it, how to test it, how to jump it, and what to do next. Whether you have a 1990 Chevy truck, van, or SUV, these steps apply to most models including the C/K series, G20 van, Blazer, and S10.

What Is the Fuel Pump Relay and Why Does It Matter?

The fuel pump relay is an electrical switch that sends battery power to the fuel pump when you turn the ignition key. In a 1990 Chevy, the relay is part of the fuel delivery system. The engine computer (ECM) controls the relay. When you turn the key to ON, the ECM grounds the relay for about two seconds to prime the fuel system. Once the engine starts and reaches 400 RPM, the ECM continues to ground the relay so the pump runs continuously .

Common symptoms of a bad fuel pump relay include:

  • Engine cranks but won't start
  • No fuel pressure at the rail
  • No sound from the fuel pump when you turn the key to ON
  • Intermittent stalling or hard starting

A bad relay is one of the easiest and cheapest problems to fix. It costs about $10 and takes just a few minutes to replace .

Where Is the Fuel Pump Relay on a 1990 Chevy?

The exact location varies by model, but here are the most common locations:

1990 Chevy C/K Series Trucks (1500, 2500, 3500): Under the hood, in the fuse/relay box near the firewall on the driver's side. Look for a small rectangular relay labeled "FUEL PUMP" or "FP" on the fuse box diagram .

1990 Chevy G20 Van: Under the hood, in the middle of the firewall, just below the rubber rear hood gasket . Some owners report it behind the doghouse (engine cover) or under the dashboard on the driver's side .

1990 Chevy Blazer 5.7: On the firewall, passenger side .

1990 Chevy S10: Under the hood, on the firewall, driver's side, close to the master cylinder . For the 1989-1990 model, it's inside the engine compartment fuse box .

1990 Chevy P30 (Motorhome/Step Van): Most commonly on the engine bay firewall near the master cylinder. Some RV manufacturers placed it under the dashboard near the steering column or behind the glove box .

Quick Tip: If you can't find the relay, look for a small black or gray plastic cube with four or five metal prongs. It's about 1 inch square. The relay is often color-coded. In some models, the green relay is the fuel pump relay, the brown is the EEC (computer) relay .

How to Test the Fuel Pump Relay

Testing the relay is simple and requires no special tools. Here are three methods:

Method 1: Listen for the Click

Turn the ignition key to ON (do not start the engine). Have a helper listen near the relay location. You should hear a single click as the relay activates. If you hear no click, the relay may not be getting power or the coil is bad .

Method 2: Swap with a Similar Relay

Many 1990 Chevy trucks use identical relays for different systems (horn, A/C, etc.). Find a relay of the same type (same part number or color) and swap it with the fuel pump relay. If the fuel pump now works, the original relay was faulty .

Method 3: Use a Multimeter

  1. Remove the relay from the socket.
  2. Set your multimeter to ohms (resistance).
  3. Check continuity between the coil terminals (usually pins 85 and 86). You should see a resistance reading (typically 50-200 ohms). If the reading is infinite (open), the coil is bad.
  4. Apply 12 volts to the coil terminals (pin 85 and 86). You should hear a click.
  5. With the relay activated, check continuity between the switch terminals (pins 30 and 87). You should have continuity (near zero ohms) .

How to Jump the Fuel Pump Relay on a 1990 Chevy Truck

Jumping the relay bypasses the relay and sends power directly to the fuel pump. This is a useful diagnostic test to see if the pump itself works.

Tools needed: A short piece of 12-gauge insulated wire, a paperclip (if you're careful), or a fused jumper wire for safety .

Step-by-step instructions:

  1. Locate the relay. Find the fuel pump relay in the under-hood fuse box (see the location section above).

  2. Remove the relay. Pull the relay straight out of the socket. You will see the socket with numbered terminals.

  3. Identify terminals 30 and 87. These are the two largest terminals in the socket. Terminal 30 is battery power, and terminal 87 connects to the fuel pump .

  4. Connect the jumper wire. Insert one end of the jumper wire into the socket for terminal 30 and the other end into terminal 87. Make sure the wire is secure.

  5. Turn the ignition to ON. Do not start the engine. You should hear the fuel pump run. If the pump runs, the relay is faulty and needs replacement. If the pump does not run, the problem is elsewhere—likely the pump itself, wiring, or a blown fuse .

Safety tips:

  • Ensure the ignition is OFF before making any connections .
  • Use a fused jumper wire for added safety to prevent short circuits .
  • Do not leave the jumper wire in place for more than a few seconds. This is a temporary test only .
  • If the pump runs but the engine still won't start, replace the faulty relay .

What to Do If the Fuel Pump Doesn't Run When Jumped

If the pump does not run after jumping the relay, the problem is likely not the relay. Here are other common causes to check:

Blown fuel pump fuse. Check the fuse box under the dash or under the hood. Look for a 15-20 amp fuse labeled "FUEL PUMP" or "FP." Replace if blown .

Bad fuel pump. The pump itself may be worn out. It is located inside the fuel tank. On a 1990 Chevy, the pump is about $60 at auto parts stores .

Corroded wiring connections. The wiring harness connector at the fuel pump is a common failure point. On a G20 van, there are two plugs for the rear fuel pump wires: one behind the dogbox opening and another on the passenger frame rail in front of the rear axle. Corrosion here is a known problem. Try unplugging and reconnecting these connectors several times .

Clogged fuel filter. A dirty fuel filter can kill GM fuel pumps. Always replace the filter when replacing the pump .

Faulty ECM. In rare cases, the engine control module fails to ground the fuel pump relay. This is less common but possible .

How to Replace the Fuel Pump Relay

Replacing the relay is straightforward:

  1. Purchase a new relay that matches the OEM specifications (AC Delco part number or equivalent). You can find them at any auto parts store for about $10 .
  2. Disconnect the negative battery cable.
  3. Remove the old relay from the relay center.
  4. Plug in the new relay, making sure it is fully seated.
  5. Reconnect the battery.
  6. Test the fuel pump by turning the ignition to ON. You should hear it prime for 2 seconds .

Recommended Fuel Pump: KEMSO

If your testing shows the relay is good but the fuel pump still does not run, you likely need to replace the fuel pump itself. For a reliable, long-lasting replacement, we recommend KEMSO brand fuel pumps.

KEMSO fuel pumps are high-performance, OEM replacement units designed to meet or exceed factory specifications. They are built with precision components that deliver consistent fuel pressure and flow under all driving conditions. Every KEMSO fuel pump comes with a lifetime warranty, so you install it once and never worry about it again. Whether you are restoring a classic 1990 Chevy truck, upgrading a daily driver, or building a performance machine, KEMSO has the right pump for your application.

To find the exact fuel pump for your 1990 Chevy, visit the KEMSO website: https://www.kemsoracing.com/

Final Thoughts

The 1990 Chevy fuel pump relay is a small part that can cause big problems. Start by locating it in the under-hood fuse box, then test it by listening for a click, swapping it with another relay, or jumping it with a wire. If the pump runs when jumped, replace the relay. If the pump still does not run, check the fuse, wiring, and fuel pump itself.

Remember to always work safely with electrical systems. Disconnect the battery before handling components, and use fused jumper wires for testing. The relay is a cheap and easy fix, but if you need a new fuel pump, trust KEMSO for quality, performance, and a lifetime warranty.

For more information and to purchase a KEMSO fuel pump for your 1990 Chevy, visit: https://www.kemsoracing.com/


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