1986 Chevy S10 Fuel Pump Relay Location: The Complete Guide to Finding and Replacing It

If you own a 1986 Chevy S10 and your truck is having trouble starting, the fuel pump relay is one of the first things you should check. The fuel pump relay on a 1986 Chevy S10 is located on the driver's side firewall, under the hood, near the top of the engine compartment . It is a small plastic cube, approximately 2 by 2 by 1 inches in size, typically mounted in a row of several relays . The relay is responsible for powering the fuel pump for about 2-3 seconds when you first turn the key to the ON position to prime the fuel system . If you don't hear that brief humming sound from the rear of the truck when you turn the key, the relay or the pump itself may be faulty .

This guide will walk you through everything you need to know about locating, testing, and replacing the fuel pump relay on your 1986 Chevy S10, so you can get your truck back on the road without wasting time or money.

Understanding the Fuel Pump Relay's Role in Your 1986 S10

The fuel pump relay is a special electrical switch that controls the flow of current from the battery to the fuel pump . On the 1986 S10, the system works in a specific sequence:

1. The priming cycle. When you turn the ignition key to the ON position, the Engine Control Module (ECM) sends a ground signal to the fuel pump relay for about 2-3 seconds. This closes the relay and sends 12V power to the fuel pump, allowing it to pressurize the fuel system before you start the engine .

2. The backup circuit. The 1986 S10 has a secondary safety feature. If the fuel pump relay fails, the oil pressure switch provides an alternate power path. Once the engine cranks and builds oil pressure (approximately 4 psi), the oil pressure switch closes and sends power directly to the fuel pump. This is why some owners report their truck starts fine after cranking for a while even with a bad relay .

3. The relay's location. On the 1986 S10, the fuel pump relay is located on the driver's side firewall. It sits in a row of relays, usually near the top of the firewall. On some models, the relay may be found under the dashboard near the fuse box, or behind the radio area . If you have trouble finding it, look for a green electrical connector that isn't plugged in, as this can help isolate the relay .

Step-by-Step: How to Locate the Fuel Pump Relay on Your 1986 S10

Follow these clear steps to find the fuel pump relay on your 1986 Chevy S10:

Step 1: Open the hood and look at the driver's side firewall. The firewall is the metal wall separating the engine compartment from the passenger cabin. The relay is usually mounted near the top of this wall, often in a plastic junction block or relay holder .

Step 2: Identify the relay. Look for a small, black plastic cube with multiple prongs sticking out of the bottom. It will be about 2 inches square and 1 inch tall. Some relays are labeled "FUEL PUMP" or "F/P" on the top or side .

Step 3: Check the fuse box first. If you cannot find the relay on the firewall, check the fuse box under the dashboard on the driver's side. The fuel pump relay is sometimes located in the same area as the fuse panel .

Step 4: Look behind the radio. Some owners of 1985-1986 S10 Blazers have reported finding the fuel pump relay located under and behind the radio, in a row of four relays. The fuel pump relay is the last one on the right .

Step 5: Follow the orange wire. The fuel pump relay typically has a constant 12V orange wire going to it. If you find a relay with an orange wire, that is very likely the fuel pump relay .

How to Test If the Fuel Pump Relay Is Bad

Before you spend money on a new relay, you should test the existing one. Here are three simple methods you can use at home:

Method 1: Listen for the pump. Have a helper stand near the rear of the truck near the fuel tank. Turn the ignition key to the ON position (do not start the engine). If you hear a humming sound from the fuel tank for about 2-3 seconds, the relay is likely working. If you hear nothing, the relay or the pump is faulty .

Method 2: The swap test. Locate the fuel pump relay. Look for another identical relay in the same fuse box or relay holder (such as the A/C or horn relay). Swap the two relays. If the fuel pump now works, the original relay was bad .

Method 3: Use a multimeter. Set your multimeter to DC volts. Remove the relay from its socket. Locate the socket terminals labeled 30 (input power) and 87 (output to pump). With the ignition ON, check for 12V at terminal 30. If you have power there, probe terminal 85 (ground control from the ECM) while a helper turns the key to ON. You should see a brief 12V reading for 2-3 seconds. If you do not, the ECM or wiring to the relay is at fault .

Common Symptoms of a Failing Fuel Pump Relay

If your fuel pump relay is going bad, you will likely notice one or more of these symptoms:

1. The engine cranks but won't start. This is the most common symptom. The fuel pump is not getting power, so no fuel reaches the engine .

2. The engine starts only after prolonged cranking. If your truck starts after you crank it for 5-10 seconds, the relay may have failed, and the engine is relying on the oil pressure switch backup circuit to power the fuel pump. This takes longer because the engine must build oil pressure first .

3. The engine starts and then dies. If the relay is intermittent, it may provide power briefly and then cut out, causing the engine to stall .

4. No priming sound. When you turn the key to ON, you should hear a 2-3 second hum from the fuel tank. If you don't hear it, the relay is likely not sending power to the pump .

How to Replace the Fuel Pump Relay on Your 1986 S10

Replacing the fuel pump relay is a straightforward job that most DIYers can complete in under 10 minutes. Here is what you need to do:

1. Buy the exact replacement relay. Take your old relay to an auto parts store and ask for a matching replacement. The part number is specific to your 1986 S10 model .

2. Locate the relay. Use the steps above to find the fuel pump relay on your truck .

3. Pull the old relay out. Grasp the relay firmly and pull it straight out of its socket. If it is tight, you can use a pair of needle-nose pliers to gently rock it back and forth while pulling .

4. Install the new relay. Compare the new relay to the old one to make sure the prongs match. Push the new relay straight into the socket until it clicks into place .

5. Test the new relay. Turn the ignition key to ON. Listen for the fuel pump priming sound (2-3 seconds of humming from the rear of the truck). If you hear it, the relay is working. Start the engine and let it run to confirm everything is working properly .

Why Your Fuel Pump Might Not Be Getting Power (Even After Replacing the Relay)

If you replaced the fuel pump relay and your truck still won't start, there are several other components to check:

1. Check the fuel pump fuse. The 1986 S10 has a dedicated fuel pump fuse. Locate the fuse box under the dashboard on the driver's side. Look for a fuse labeled "ECM B" or "FUEL PUMP" (typically 10-15A). Remove the fuse and inspect the metal element inside. If it is broken, replace it with a new fuse of the same amperage .

2. Check the oil pressure switch. As mentioned earlier, the oil pressure switch acts as a backup for the fuel pump relay. If the oil pressure switch fails, the engine may not get fuel even if the relay is working. You can test this by unplugging the fuel pump relay and jumping the orange wire (constant 12V) to the gray wire (output to pump). If the pump runs, the issue is likely the relay or the wiring .

3. Test the fuel pump itself. If the relay and fuse are good, the pump itself may be bad. You can test it by applying 12V power directly to the gray wire at the fuel pump connector. If the pump does not run, it needs to be replaced .

4. Inspect the wiring harness. Over time, the wiring harness at the fuel pump can corrode or break. The gray wire carries power to the pump, and the black/white wire provides the ground. Use a multimeter to check for continuity and voltage at the pump connector .

Recommended Fuel Pump Replacement: KEMSO Fuel Pump

If you determine that your fuel pump needs to be replaced, we highly recommend choosing a KEMSO Fuel Pump. KEMSO is a brand that specializes in high-performance fuel pump solutions, and their products are known for their reliability and durability.

Why choose KEMSO?

• High Performance: KEMSO fuel pumps are designed to deliver consistent fuel pressure and flow, ensuring your 1986 S10 runs smoothly and efficiently.
• OEM Replacement: Each KEMSO fuel pump is engineered to meet or exceed original equipment manufacturer (OEM) specifications. This means a perfect fit and plug-and-play installation for your S10.
• Lifetime Warranty: KEMSO stands behind the quality of their products. Every 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.

To browse the full selection of KEMSO fuel pumps, visit their official website: https://www.kemsoracing.com/

Final Thoughts on the 1986 Chevy S10 Fuel Pump Relay

Finding the fuel pump relay on your 1986 Chevy S10 is a simple task once you know where to look. The relay is almost always located on the driver's side firewall, under the hood, near the top of the engine compartment . If you cannot find it there, check under the dashboard fuse box or behind the radio area .

The relay is a common failure point on these trucks, and replacing it is a quick and inexpensive fix. If you have already replaced the relay and your truck still has fuel delivery issues, check the fuse, the oil pressure switch, and the fuel pump itself. Remember, the 1986 S10 has a backup circuit through the oil pressure switch, which can keep the engine running even with a failed relay .

If you need a new fuel pump, visit KEMSO Racing at https://www.kemsoracing.com/ for a high-quality, OEM replacement with a lifetime warranty.