Fuel Pump Wiring Basics

peering into an automotive fuel pump

The fuel pump wiring is a critical part of any vehicle. It is the device by which fuel is delivered to the engine. If the fuel pump wiring is not done correctly, the pump will not work, and the engine will not run. There are two types of fuel pumps: those that mount inside the fuel tank itself (standard pump), and those that mount underneath the car, just in front of the fuel tank (inline pump).

Basic Components

The basic components of an electric fuel pump are the positive and negative (ground) electrical terminals on the pump itself, the fuel sending unit, the relay switch for the pump, and the fuse for the fuel pump in your vehicle’s fuse box. Electricity can be dangerous. Please make SURE that the car battery is completely disconnected and that the fuse for the fuel pump (found in the fuse box) is removed. Electricity should not be taken lightly. A spark from a loose wire can ignite fuel vapors resulting in a major catastrophe. Be careful.

Electrical Connections

The first tip for wiring a fuel pump has to do with the electrical connections on the pump itself. Make sure you label the positive and negative (ground) wires on the fuel pump. This is a basic task you should always do when working with electrical components on your car to avoid being shocked, causing sparks, or frying components. Missing this very simple part of the wiring process can instantly ruin the entire pump (and possibly the entire electrical system) once you start the car. A small piece of masking tape wrapped around the wire and labeled with a "+" and "-" will do the trick.

Physical Wiring

automotive fuel pump

After making sure that the battery is disconnected and the fuse is removed from the fuse box, connect the wires to the appropriate places. The positive wire coming from the fuel pump can now be connected to the positive wire coming from your vehicle's wiring harness. Make sure the connection is tight and secure. A loose connection will generate heat at the site of the connection and not supply proper voltage to the pump, which likely will burn the wire and damage the pump, causing your engine to run poorly, if at all.

Take the ground wire from the fuel pump and attach it to the nearest electrical ground surface you can find (usually the frame of your car). When attaching the ground wire, make sure the connector on the end of the wire and the area where you are attaching it are clean and rust free. Also make sure the connection is secure and tight. As mentioned before, a loose connection can generate heat on the wire and disrupt the voltage supply to the pump causing it to not function properly.

Fuel Pump Wiring FAQ

What happens when you wire a fuel pump wrong?

If the fuel pump on a vehicle is not wired correctly, the pump may not receive enough voltage. As a result, the pump will turn more slowly.

This will affect the vehicle by not providing maximum fuel efficiency and it will put more strain on the pump, which will ultimately shorten its life.

Why does a fuel pump have 4 wires?

Many fuel pump designs have four wires, two of which sense the fuel level of the vehicle and larger wires that provide the fuel flow to the pump.

Does the ignition switch control the fuel pump?

The ignition switch provides the initial power to the fuel pump that allows the vehicle to start. If the vehicle is not starting properly due to an ignition failure, the fuel pump will also fail and the engine will fail to "spark."

How do I know if my fuel pump is getting power?

There are multiple things that might fail which can prevent power from getting to the fuel pump. You will want to test the ignition switch, the fuel pump relay, or the fuse that powers the pump.

What would cause me not to get power to my fuel pump?

Rusted or loose connections and damaged wiring can cause a fuel pump to stop receiving power.