https://www.thedrive.com/maintenance...o-test-a-relay


And

 

First, know how a relay works then how to test is obvious. Pin numbers are universal.

 

A relay can pass resistance checks and still be bad. Even if it clicks does not mean it powered the circuit. The points that make contact can be burnt.

 

That is why you check continuity and voltage on both sides. Clicking just tells that the solenoid part is working. Yes, I said it.

 

If they have burnt contacts then no continuity

 

We just swap them out rather than doing all that. Wiring problems require that kind of testing.

 

And then the new/swapped relay burns out because it turned out to be a circuit problem.
But yes, that is what a flat rate mechanic would do; much more money in swapping parts instead of doing the work they are getting paid to do, an hour of diagnostic time for 4 minutes work. Then if it turns out to not be the relay charge the customer for the parts because "electrical parts are non-returnable". Been there, done that; a Ford dealer replaced all of the emissions sensors because they were listed as "possible causes", couldn't be bothered to do testing. Stated symptoms "CEL on, heater blowing cold air, running rough"; it was a stuck open t-stat, ambient temperature 15F.

 

Have you ever seen this? I haven't. Think about what that would mean. You would be pulling enough current through a 22 gauge wire to burn up the coil. I don't think that is possible. Also there should be a fuse to blow in the process.

 

That's what any certified technician would do. It's taught in the class room.

 

You have never worked in a busy shop. You may not have worked in any shop but your own. We have several relays in every bay for techs to use for swapping out. It's fast and easy and it it works good and it it doesn't the relay goes back and we proceed to other testing. That's the way it's done in any decent garage.