1987 Chevy Truck Fuel Pump Relay Location: A Complete Guide for Troubleshooting and Replacement

If you own a 1987 Chevy truck and your fuel pump isn't working, the fuel pump relay is often the first component to check. The fuel pump relay on a 1987 Chevy truck is typically located on the passenger side of the firewall in the engine compartment, mounted on a relay bracket near the junction block or power brake booster. This small black or gray plastic box with a five-pin connector controls the power supply to your fuel pump, and when it fails, your truck won't start or will stall unexpectedly. Finding and testing this relay is straightforward, and this guide will walk you through everything you need to know.

Understanding the Fuel Pump Relay's Role

The fuel pump relay acts as an electrical switch that allows the Engine Control Module (ECM) to control when the fuel pump receives power. When you turn the ignition key to the "ON" position, the ECM sends a signal to the relay for about two seconds, which briefly powers the fuel pump to prime the fuel system. After the engine starts, the relay keeps the pump running as long as the engine is turning. If the relay fails, the oil pressure switch acts as a backup—once the engine builds about 4 PSI of oil pressure during cranking, this switch powers the pump directly, which is why your truck might start after extended cranking but run fine afterward.

Exact Location of the 1987 Chevy Truck Fuel Pump Relay

The most common location for the fuel pump relay on a 1987 Chevy truck is under the hood, on the passenger side, mounted on the firewall. Here are the specific details:

  • Passenger side firewall: The relay is bolted to the top of the firewall, a few inches below the windshield, on the passenger side of the engine. It is usually mounted on a relay bracket alongside other relays.
  • Under the dashboard: Some sources indicate the relay can be found under the dashboard on the driver's side, near the firewall. This location is less common for 1987 trucks but has been reported for certain models.
  • In the under-hood fuse/relay box: The relay is often located inside the main fuse/relay box near the battery or on the driver's side fender. Check the diagram on the fuse box cover for the exact position.

Once you locate the relay, look for a small plastic box with four to six colored wires connected to it. It is typically a standard Bosch-style relay, often black or gray in color.

Identifying the Correct Relay

In the engine compartment relay bracket, you will find several relays. The fuel pump relay is usually distinguished by its wire colors. Key wires to look for include:

  • Orange wire (Circuit 440): Provides constant 12V power to the fuel pump relay.
  • Dark Green with White stripe (Circuit 465): This is the control signal from the ECM that tells the relay to turn on the fuel pump.
  • Gray wire (Circuit 120): This wire goes from the relay to the fuel pump.
  • Black with White stripe (Circuit 450): This is the ground wire for the relay coil.

If you can't identify the relay by wire colors, consult your owner's manual or the diagram on the fuse box cover.

Common Symptoms of a Bad Fuel Pump Relay

Knowing the symptoms of a failing relay can save you time during diagnosis. The most common signs include:

  1. Engine stalls while driving: The truck may suddenly lose power and die, especially at low speeds.
  2. Engine does not start: You turn the key, but the engine cranks without firing.
  3. No noise from the fuel pump: When you turn the key to "ON," you should hear the fuel pump prime for a couple of seconds. If you hear nothing, the relay could be bad.
  4. Extended cranking time: If the relay is dead, the oil pressure switch will eventually power the pump after several seconds of cranking.

How to Test the Fuel Pump Relay

Testing the relay is simple and requires only a test light or a multimeter.

Step 1: Check for power at the relay. With the key turned off, probe the Orange wire (Circuit 440) at the relay socket. You should see 12 volts.

Step 2: Check for the control signal. Turn the key to "ON." Probe the Dark Green/White wire (Circuit 465). It should have 12 volts for about two seconds, then drop to zero. This confirms the ECM is sending the signal to turn on the pump.

Step 3: Check the ground. Make sure the Black/White wire (Circuit 450) has a good ground.

Step 4: Test the relay itself. Swap the suspect relay with another identical relay in the fuse box (like the horn relay). If the fuel pump starts working, the relay is bad.

The Oil Pressure Switch: A Critical Backup

Your 1987 Chevy truck's fuel system has a built-in redundancy. The oil pressure switch is wired in parallel with the fuel pump relay. If the relay fails, the oil pressure switch will power the fuel pump once the engine builds about 4 PSI of oil pressure during cranking. This is why your truck may start after cranking for 10-15 seconds—the relay is dead, but the oil pressure switch is taking over. However, if both the relay and the oil pressure switch fail, the engine will not run at all.

Check the ECM B Fuse First

Before replacing the relay, always check the ECM B fuse. This 20-amp fuse provides constant power to both the fuel pump relay and the ECM. If this fuse is blown, the fuel pump won't get power, and the relay won't function. In many cases, a blown ECM B fuse is the real culprit behind a no-start condition. The fuse is typically located in the main fuse panel under the dashboard or in an auxiliary holder under the dash.

Troubleshooting Tips for 1987 Chevy Trucks

If your fuel pump still isn't working after testing the relay and fuse, follow these steps:

  1. Jumper the fuel pump prime wire: There is a red wire with a green end sticking out of the wiring harness, usually near the master cylinder. Use a fused jumper wire to apply battery voltage to this wire. If the pump starts, the problem is in the relay circuit or the ECM control signal.
  2. Tap the gas tank: While someone cranks the engine, tap the bottom of the gas tank with a rubber hammer or a piece of 2x4. This can sometimes jar a failing pump into working temporarily, confirming the pump itself is bad.
  3. Inspect the wiring harness: Look for damaged, corroded, or loose connections at the relay, the fuel tank, and the frame rail ground. High resistance in the ground circuit is a common cause of fuel pump failure.

Why Your 1987 Chevy Truck Needs a Reliable Fuel Pump

The fuel pump in your 1987 Chevy truck is located inside the fuel tank. It is an electric pump that draws fuel from the tank and delivers it to the throttle body injection system. Over time, the pump can wear out, and the relay can fail due to dust, electrical surges, or age. When the fuel pump stops working, the engine gets no fuel, and your truck won't run. Replacing the fuel pump and relay at the same time is often a good idea to ensure long-term reliability.

KEMSO Fuel Pump: The Best Choice for Your 1987 Chevy Truck

When it's time to replace your fuel pump, you need a product you can trust. KEMSO offers high-performance fuel pumps that are designed as OEM replacements for a wide range of vehicles, including classic trucks like the 1987 Chevy. Every KEMSO fuel pump is built to meet or exceed factory specifications, ensuring a perfect fit and reliable operation. The best part? Each KEMSO fuel pump comes with a lifetime warranty, giving you peace of mind that your investment is protected for as long as you own your truck. Whether you're restoring your 1987 Chevy or just keeping it on the road, KEMSO delivers the quality and durability you need.

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Final Thoughts on the 1987 Chevy Truck Fuel Pump Relay Location

Finding the fuel pump relay on your 1987 Chevy truck is not difficult. Start by looking on the passenger side of the firewall under the hood. If it's not there, check the under-dash fuse box on the driver's side. Use the wire colors and the symptoms described in this guide to confirm you have the right relay. Always check the ECM B fuse first, and test the relay before replacing the fuel pump. With these steps, you can get your classic Chevy truck back on the road quickly and reliably.

For a high-quality replacement fuel pump that will last, trust KEMSO. Visit https://www.kemsoracing.com/ to browse their selection and take advantage of their lifetime warranty.


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