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I had a question about relays...spurred on by a thread below


schivvers
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I do like the pull-a-part junkyard and am wondering how i can verify that a relay is good before i purchase and install it? Is there a way to do that in the field as it were? Thanks...I know someone here has an answer for me...Thank you in advance.

Dave

'76 '02 in the early stages of rebirth.

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Hey, thanks.

This works if the car has power...I was wondering if there was a way to test them with a different type of setup. Also I realize they are inexpensive but I had some uses outside of the realm of my car that I was querrying about.

Cheers.

And thanks for responding.

Dave

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Guest Anonymous

Dave ... you can test them out of the vehicle with a DMM and a battery. If you remove one and look at the schematic molded into the plastic relay housing, it depicts the internal circuitry. Set your DMM on continuity test and put the leads on the coil terminals. There should be a beep indicating that the coil is not burned out.

Then find the contact terminals. A continuity test should produce a 'beep' if the contacts are NC (normally closed) and no beep if the contacts are NO (normally open).

Energize the relay coil with 12v and the results should revese. The NC contacts become open and indicate an open circuit with the DMM. The NO contacts become closed and indicate a closed path with the DMM continutiy test.

If you are testing a 5-pin relay, unenergized the relay shows continutiy for the NC pair and 'open' circuit for the NO pair. When the coil is energized these measurements reverse. The test is between the 'common' terminal and the NO, and NC.

Good Luck!

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Guest Anonymous

I guess when you're switching mega current for motor windings with 'contactor' size relays, pitting of the contacts etc. is an issue. But the little 'ice cubes' that are in our car for horn and lamps probably won't need a high current test with full voltage. Corroded contacts are resistive and show excessive resistance when tested with a DMM. Probably should have mentioned it.

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