A fuel pump relay is like any other relay in terms of function. A relay uses a fairly low-power electrical signal to close a circuit that sends power to high-amperage devices like the starter, electric fans, A/C fan and fuel pump. Relays aren't technically necessary, but manufacturers use them to centralize the electrical control system in a small area and to reduce the amount of necessary heavy-duty wiring. Testing a relay is a simple procedure, requiring only a few minutes and the most basic of shop materials.
Things You'll Need
- Basic hand tools
- 12-gauge wire
- Wire strippers
- Utility knife
- Electrical tape
- Test light
Pull the fuel pump relay out, flip it over and identify the terminals. You should see four terminals; two are ground terminals and two are positive. You'll notice that one of the terminals sits at a 90-degree angle to the others; this is the power-in (positive) terminal from the control device. The one opposite it is the control device ground, and the ones on either side are the circuit that goes to the fuel pump.
Cut two lengths of red and black wire, each about two feet long. Strip about two inches of insulation from either end of each wire. Rotate the relay so that the control-input terminal sits at the 12 o'clock position. Wrap the exposed copper of one of your red jumper wire tightly around this terminal, then wrap the terminal with electrical tape. Cover all of the exposed metal with tape, and make sure the wire's secure.
Wrap the exposed copper of your black jumper wire around the terminal opposite the control input and the terminal on the right. Put another way, connect one end of the black wire to the terminals at the 3 o'clock and 6 o'clock positions. Secure it with electrical tape and cover all of the exposed metal. At this point, only the terminal on the left (the 9 o'clock position) is exposed.
Tape the other end of your red jumper wire to the positive battery terminal. Carefully lower the other end of your black jumper onto the negative battery terminal and listen for a click as the wire makes contact. This click is the sound of the relay closing, and it's a good sign. Lift the black wire off of the battery terminal.
Connect your test light's alligator clip to the exposed terminal on the relay and press the test light's tip into the top of the negative battery terminal. If the light comes on when you touch it to the battery, then the terminal is stuck shut and it's no good. The light should only come on when you touch the black wire to the negative battery terminal. If the light doesn't come on when you touch the wire to the terminal then the relay is no good.
Tips & Warnings
- If you don't have a working test light and don't mind irritating your significant other, you can make a test light out of an old string of Christmas tree lights. Just cut three-foot section out of the tree lights, strip the ends and use it in place of the black wire. If the relay works, the lights will add some festive if temporary illumination to your engine compartment. Bear in mind this only works with series-wired (single-wire) light strands, and only if none of the bulbs are blown. You could also use a digital multimeter (set to read voltage) in place of the black wire, but it's not as much fun.
- For five-terminal relays, the center terminal does the same thing as the sideways-clocked terminal at the 12 o'clock position.
- "Auto Fundamentals"; Martin T. Stockel, Chris Johanson; 2000
- Autoshop 101: Understanding Relays
- Photo Credit Jupiterimages/Photos.com/Getty Images
Where Is the Fuel Pump Relay Located?
The fuel-pump relay unit is responsible for turning the fuel pump on when it detects the engine is running. When the ignition...
What Is a Fuel Pump Relay Switch?
The fuel pump relay switch gets the fuel pump running in the vehicle during the start cycle. The terms fuel pump relay...
How to Replace a Fuel Pump in a Ford F-150
The fuel pump on your Ford F-150 is inside the fuel tank. This allows the pump to build the high pressure needed...
How to Wire a 5 Connector Relay
A five connector automotive relay, generally used to operate accessories that draw more than 30 amps, connects through a pre-wired relay socket....
How to Test a Fuel Pump
In the lifetime of owning a vehicle it is very possible that you may at some point need to test your fuel...
How to Determine If a Fuel Pump Relay Is Bad
A car's fuel pump relay turns on the fuel pump when the motor runs. When a relay is defective, it is usually...
How to Replace the Fuel Pump on a 1998 Jeep Wrangler
The 1998 Jeep Wrangler's engine receives fuel from the fuel tank by means of an electrically powered fuel pump assembly located in...
How to Replace a Fuel Pump in a 92 Accord
The Honda Accord is one of the most popular vehicles on the road today. In fact, Edmunds sites the Accord as an...
How to Test a Fuel Pump Relay on a 2002 GMC Yukon Denali
The fuel system in the 2002 GMC Yukon has several electronic checking points. One of those checking points is the fuel pump...
How to Check a Fuel Pump Relay
A fuel pump relay's job is to take some of the voltage load off of the wiring harness to allow a better...
How to Check if a Fuel Pump Is Bad
When checking to see if a fuel pump is bad, make sure there's fuel in the tank, use a gauge to check...