Tips from the pros when testing electrical relays in cars


Automotive relays are employed extensively across almost all of your vehicle’s electrical systems. If you were to ask an Electrician Southend way they would know all about wires, electrics, Functioning as a buffer between two circuits of different amperage, relays allow you to control a device where the existing circuit or inline switch lacks the capacity to tolerate the current required.

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For example, car radiator fans can create a load of more than 20 amps. If connected directly to the computer that controls the fan, this level of current would burn out the circuit.

Relay testing: step-by-step guide

1.      Before heading for the relays, check that all fuses are operational with a test light and replace any faulty ones.

2.      Examine the cover of the power distribution centre (PDC) for schematics showing relay locations. If this is not visible, consult the owner’s manual.

3.      Gently touch the relay to be tested and get someone to turn the key in the ignition. You should feel a click as the relay switches on. If so, your test is complete and the relay is working. If not, go on to step 4.

If you feel a click from the relay but the circuit it controls is still not working, the contacts in the relay have likely shorted and the component will need to be replaced.

4.      Taking note of the relay’s orientation in the PDC, take hold of the relay and pull it out. Some slight wiggling may be required.

5.      Holding the relay, examine its metal terminals for any indications of corrosion or heat damage. If any is present, the relay should be replaced.

6.      With the relay still removed, inspect the relay housing on the PDC. Often made from plastic, the housing can melt or distort when overheated. This can occur due to resistance from a poor connection or overloading.

7.      Scrape away any corrosion with an appropriately sized metal tool to make sure there will be a good connection when the relay is replaced.

8.      Replace the relay, making sure to install it in the correct orientation.

Other options

9.      If the circuit still fails, test the automotive wiring looms for power with a grounded test light. If power is lacking, replacement wiring harnesses are available.
10.     If the test for power is successful, the accessory powered by the circuit is likely the problem.

Written by suNCh8

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