• How to test electrical relays

    Relays are commonly used as a switching device. A relay has a coil inside that when energized will actuate the contacts and transfer current from the input contacts to the output contacts. The internal coil has a power input and a ground. It takes both the power and ground to operate. Most relays will either be waiting on a power input or a ground connection.

    Relay Test

    Step 1- Find the relay's normal coil resistance.

    This is the amount of resistance from the coil's power input to the coil's ground input. You might find this information in the service manual of the component the relay goes to, or by researching on the internet.

    Power Relay

    Car Relay

    Step 2- Locate the power and ground contacts of the coil.

    Find the two contacts of the relay which are commonly numbered x1 and x2. The power contact supplies voltage to energize the coil, and the other contact supplies the ground.

    Step 3- Test the resistance of the coil.

    Place your multimeter in the Ohms resistance setting and touch a meter lead probe to each contact found in step 2. The reading should be some amount of resistance across the coil. Compare your reading with the relay's standard resistance found in step 1.

    Step 4- Review the test results.

    If you measured no movement, or an O.L., then the relay is electrically open. If you measured close to zero Ohms, then the relay coil is shorted to ground.

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