Testing a relay for continuity?

[SDMAN1981]

When testing for continuity on a car relay what is acceptable resistance in the cars relay switch?

Topic

[Wayne]

Around 6:47:

If at all fuzzy on relay workings:
http://www.the12volt.com/relays/relays.asp

There really should only be whatever you see in your leads resistance wise (or barely over it) for contacts that are closed (30 and 87 when 85 and 86 is energized). More of a judgment call, I’ve only seen a resistance check like this work once myself on a failing but not dead relay. Opening and closing the coil circuit (85 and 86) a few times showed a large and fairly obvious discrepancy on the last test operation, near a kohm at the time.

In the very rare instances where I’d truly suspect an issue with a relay (they’re usually rated and tested for several million operations before failing), it’s far easier to just swap it with another on the vehicle to see. Nearly always others in the fuse-box to swap with that are the same size, and amperage rating for OEM relays on the vehicle to use. Just needs to be from something non-critical, such as AC or something.

[EricTheCarGuy]

The above post pretty much covers it. Honestly, I prefer voltage drop checks over resistance checks as they measure what’s happening in a ‘live’ circuit. That said, continuity testing is also valid. More info here.

http://www.ericthecarguy.com/faq/solving-automotive-electrical-problems

[Author]

Replies