How to Check a Car Relay Circuit

Written by michael cantrell
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How to Check a Car Relay Circuit

Your car uses many different types of electronic, wiring and relay systems to help various accessories function properly. If you experience problems with specific electronic accessories in your vehicle, it is time to run a test on your car's relay circuits to see if one of them may be faulty. These relays can affect a wide range of parts on your car, so doing the proper testing is important to making sure your car runs smoothly.

Skill level:

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Things you need

  • Test light
  • Wire
  • Bulb and socket
  • Helper

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  1. 1

    Collect all the necessary tools. You will need a bulb and socket, a test light (tells you if a fuse is working properly or not) and possibly a piece of wire.

  2. 2

    Test all the fuses using your test light tool. Make sure you check all the fuses under the dash as well as under the hood. If all the fuses seem to be working properly, continue on with the testing.

  3. 3

    Have someone turn the key in the starter from "on" to "crank" while you carefully place your fingers on the relay that you suspect isn't working. You should feel something clicking in the relay when the engine goes from "on" to "crank." If you feel no click, you need to check the relay connections.

  4. 4

    Check the connections for any signs of overheating or of corrosion. If there appears to be any damage, use a brand-new relay. Then retest the relay to see if it is working properly (Step 3). If this fails to work, keep on testing.

  5. 5

    Check all of the terminal sockets. Connect your test light tool to the ground wire or black lead. Have your help turn the key to "on," but without turning on the engine. Using the probe from your test light, check the terminal sockets inside of the relay connector. You need to have two of these to be working properly.

  6. 6

    Consult your repair manual for detailed diagrams about replacing any damaged relays you may have.

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