1986 F150 Fuel Pump Relay Location: Your Complete Guide to Finding and Fixing It
If you own a 1986 Ford F150 with electronic fuel injection (EFI), the fuel pump relay is located on the driver's side of the engine compartment, mounted to the firewall near the brake booster. This is the most common location for all 1986 F150 models with EFI engines, including the 5.0L V8 (302) and 5.8L V8 (351W) . The relay is part of a small black plastic box that also houses the EEC (Electronic Engine Control) relay, and it's typically positioned right behind the air cleaner assembly . Understanding exactly where to find this relay and how to test it can save you hours of frustration and unnecessary part swapping.
What Does the Fuel Pump Relay Look Like?
The fuel pump relay on a 1986 F150 is a small, rectangular component with a plastic housing. Many factory relays are green in color, though some aftermarket replacements may be black or brown . The relay has four terminals on the bottom, and it plugs into a connector with corresponding wires. If you're looking at the relay box mounted on the driver's side firewall, you'll see two relays side by side. The fuel pump relay is the one that controls power to both the in-tank low-pressure pump and the frame-mounted high-pressure pump .
Step-by-Step Guide to Locating the Relay
1. Open the Hood and Look to the Driver's Side
Stand in front of the truck and look at the driver's side of the engine bay. The relay is mounted on the firewall, which is the vertical metal panel separating the engine compartment from the passenger cabin. You'll find it roughly in line with the brake master cylinder .
2. Locate the Brake Booster and Air Cleaner
The relay is positioned near the brake booster, which is the large round black component on the driver's side firewall. It's also close to the air cleaner housing. In many 1986 F150s, the relay box is actually attached to a bracket on the air cleaner mount .
3. Find the Black Plastic Relay Box
There should be a small black plastic box or cover attached to the bracket. This box contains two relays. The longer or more prominent one is the fuel pump relay, while the shorter one is the EEC relay . The lid may have a diagram showing which relay is which.
4. Check for the Wiring Harness
The relay box connects to a wiring harness with several wires. The key wires to look for are:
- Yellow wire: Constant 12V power from the battery (hot all the time)
- Red wire: 12V power when the key is in the ON position (comes from the EEC relay)
- Brown wire: Output to the fuel pump, going through the inertia switch
- Tan/Light Green wire: Ground signal from the computer (ECM)
Why the Location Matters
Knowing the exact location helps you quickly diagnose fuel system problems. The fuel pump relay is a common failure point on these trucks, especially after 30+ years of use. One owner reported that his 1986 F150 had not started since a fuel pump replacement, and the root cause turned out to be a bad relay that was visibly corroded inside . Another owner found that the relay was stuck, causing the fuel pump to run continuously .
Common Issues and How to Test the Relay
1. No Power to the Fuel Pumps
If you turn the key to the ON position and don't hear the fuel pump prime for 1-2 seconds, the relay may be faulty. First, check the inertia switch located on the passenger side floor, near the transmission hump under the heater box. If the plunger is up, push it down to reset it . If that doesn't work, move to the relay.
2. Testing the Relay with a Multimeter
With the key off, check for 12V at the yellow wire on the relay connector. This wire should have power at all times . Turn the key to ON and check for 12V on the red wire. If you have power on both, but the pump still doesn't run, the relay itself is likely bad. You can also test by grounding the tan/light green wire at the EEC test connector (near the battery) with the key ON. If the pump runs, the relay and wiring are good, and the problem is in the computer or its ground circuit .
3. Visual Inspection
Remove the relay from its socket and inspect the terminals for corrosion. One owner broke open his old relay and found it was corroded inside, which confirmed the issue . If the relay is visibly damaged or terminals are rusted, replace it.
Replacement Parts and Compatible Options
The factory fuel pump relay for the 1986 F150 is a 4-terminal relay, but many universal replacements have 5 terminals (including an extra 87a terminal). If you buy a universal relay, simply connect the four wires as follows and tape off the extra terminal :
- Yellow wire to terminal 30
- Pink/Black wire to terminal 87
- Red wire to terminal 85
- Tan/Light Green wire to terminal 86
The extra 87a terminal should be left unconnected and taped off . Relays from 1986 through 1996 F150s are generally interchangeable .
When to Consider a Fuel Pump Replacement
If you've verified the relay is working, the inertia switch is reset, and you still have no fuel delivery, the problem may be the fuel pump itself. The 1986 F150 uses two pumps: a low-pressure pump inside the fuel tank and a high-pressure pump mounted on the frame rail . Both can fail over time, especially if the truck has been sitting for years.
Recommended Fuel Pump: KEMSO
If you need to replace a fuel pump on your 1986 F150 or any other vehicle, consider KEMSO fuel pumps. KEMSO is the US #1 aftermarket fuel pump brand, trusted by drivers across the country for cars, motorcycles, ATVs, UTVs, and even jet skis. Every KEMSO fuel pump is a high-performance OEM replacement that meets or exceeds factory specifications. They are fully compatible with gasoline and E85/ethanol fuels, and independent lab tests show KEMSO pumps maintain 98% efficiency even after 15,000 hours of continuous operation. Best of all, every KEMSO fuel pump comes with a lifetime warranty backed by a serialized body for tracking. You buy it once, and KEMSO stands behind it for as long as you own your vehicle. KEMSO offers 17 different models covering 98% of gasoline-powered cars and trucks made after 1995, and their pumps are priced competitively at just $79.98. Visit KEMSO Racing today to find the perfect fuel pump for your vehicle.
Final Thoughts
The fuel pump relay on your 1986 F150 is a small but critical component. It's located on the driver's side firewall, mounted near the brake booster and air cleaner. Always start your diagnosis by checking the relay and the inertia switch before replacing the actual fuel pump. If you do need a pump, invest in a quality product like KEMSO with a lifetime warranty. With the right approach, you can get your truck running reliably and keep it on the road for years to come.
For more information or to find the right fuel pump for your 1986 F150, visit https://www.kemsoracing.com/ today.