Auto Repair & Mechanics : How to Test a Car Relay

Testing a car relay involves the use of a 12-volt source, such as a car battery, and a multimeter that is capable of reading resistance. Find out how to listen for clicks and tones that indicate a functioning relay with help from an auto mechanic in this free video on car repairs and mechanics.

Expert: J.B. Hebert
Bio: J.B. Hebert is a machinist, metal fabricator, and auto mechanic who has been fixing and modifying all things mechanical for over 20 years.
Filmmaker: David Pakman

[freakshow]

@wildabeast - it does tell you...if the relay is good, then when you apply voltage to the coil, you'll hear a click (the switch macking contact, allowing voltage across and into the rest of the circuit) and the Fluke Meter, when set to continuity check will beep (like in the video) If you get neither a click or a beep, it's a bad relay

[NPAutoRepair]

all about relays. this is very interesting and easy to understand. :) highly recommended video

[thesetruths]

Before removing (or if stuck), or afterward, try aggressively tapping, shaking and wonking them on table. Sometimes they are stuck with corrosion. You can also carefully drill holes into sides and top and spray silicone juice into them. Or wd40 (let soak and tap on it) and then brake cleaner if need be.

[looncraz]

I prefer to test 12V relays with a standard 9V battery - that way if they are weak they won't trigger properly and you know to replace it.

[hp]

@dan185z did u get it fix, was it the brake ligth switch or something

[flightmaster]

I work on F-16's and we have a relay tester I'm thinking about making one. Just take a relay block from a car and have inputs from battery and outputs to a green light so when you push a button the light lights up if it works. idk. Seems easier in the long run.

[SnookmanLJ]

Awesome video dude, extremely helpful.

[MrJummy]

You can also use an universal 110v or 220v charger which is set at 12v to test a relay.

[norwegcat]

Great video! Found it very useful - especially today. thanks!

[facestomp]

I'm guessing that if I don't have access to a meter to do this that I could do it and just listen for the click and that would tell me that the relay is functioning properly? Or would it still be a possibility that it could still be defective even though it clicks?

[freakshow]

as far as seeing - If the neter shows infinity, it is still an open circuit, even after applying power to the coil inside the relay

[goemon]

thanks a lot for this info!
i was wondering how to tell what number each terminal is on my relays till i noticed them written very small on the underside heh

[andrewbird]

What if the relay is on the vehicle, it gives an audible clicking sound when the door is open, but no continuity tone prior to that. I assume the relay is the battery saver relay. does this relay have to be working correctly for the car to start because the car does not start?

[LucasBorntreger]

Is it possible that in the process of removing/installing these relays I may have bumped one and made it suddenly work?

[munchende]

The central locking sysytem has a problem..does it mean that the relay is damaged if so how do i locate the relay the vehicle is a ford windstar 1996, and the knoba keeps going up and down till the battery is drained

[laphong]

Request for videos if the won't start ?. The battery is 12.5V and all connections.are clean. what is the next thing to do ?. Thanks

[Nettikturbo]

I'm confused. if I hear the relay click when I apply the 12 volt source, if the relay trips is there still a chance that the relay isn't working?

[ng]

You just need some AA or AAA's too, not a car battery. For 5 pole you'll want a switch that breaks power to the coil and alternately couples the test lead between 87 and 87a. Obviously those two circuits need to be isolated but by activating with a single switch you just have to e.g., with a push button, plug in relay, listen for tone, then push button, listen for tone, rinse and repeat.

[pedrovelaz]

Hello i have a question would a bad relay or missed placed relay in a 89 cadillac make the car not want to start everything works the battery is charged though it was that wasnt then thought it was gas not that either messed with the relays days before this happend and now doesnt want to start let me know thank you

[TheMcs]

Can you test a relay with power probe 3 if you can do a video using that that would be great