There are various types of relays on every vehicle, and they're not all wired in the same way, but the first step would be to go to the fuse box to find the appropriate circuit. Find out how to use one relay to test another with help from an ASE-certified mechanic in this free video on troubleshooting car problems.
Good afternoon, my name is Tom Brintzenhofe, a Certified Master Mechanic our of Redding, Pennsylvania and today we're going to talk a little bit of how to check to see if your relay is bad. Now on every vehicle, unfortunately there is this various types of relays. You have small relays; larger relays; relays controlling your, your power door locks, your power seats; you have relays controlling your starter, ignition system. So every relay is actually a little different on your vehicle. They're all wired; they're not all wired identically; so for me to sit here and explain to you how to diagnose each individual relay on every car would be a little difficult. But I'm going to try to explain to you the easiest way to find out if, if your relay is bad; if you have an, an incline that your relay is bad. If you look in your fuse box, there's this several different types of of relays in here but you have to find the one that is actually for the circuit that you're looking at. We'll say this one is your starter relay; now on the back of your C, several different prongs are on here; you have a set for the power supply; you'll have a set coming from the computer and then you have a ground that's usually activated by the computer that they click as relay on. Now what happens basically is if you're looking to turn on basically your starter; this thing would be live pretty much all the way around and when you go turn the key on, it'll ground the circuit out here and it makes the power float through down to your starter. For me to see here and explain to you how is this all wired down here, it'll be a little rough; so the easiest way I could tell you is every fuse box, like I said has several different relays in it; ninety percent of the time or ninety nine percent of the time there's more than one relay in here that is identical. So if you think you have one relay bad, the best thing I tell you is grab the one right next to it, they'll all numbered on the top and ninety percent of the time, I guess that you have one that's identical to that one and just switch it in the next spot. You'll know right off the bet when you go to try to start it then, well that relay is bad when you put a, another one over that's known as, that's actually good. So that's the easiest way I could tell you how to diagnose a bad relay.