Trying to figure out how to troubleshoot a problem with a relay. It came with a set of Hella XL auxiliary low beams that I have mounted to provide a bit of extra light up front. It's a pretty standard Bosch-type relay, but with a fuse onboard, 15 amp is what it came with. I had the truck parked at the airport for a week, came back and the Hellas weren't working. I pulled the fuse and replaced it with a new one, it blew immediately. Bad relay, or is there something else I should consider as a cause?

 

Ground maybe?I would think because of the fuse blows immediately. Check all the wires to the lights and such. So check mack sure ground is good and make sure teh power wire to to the lights is not damaged.

Sean

 

Sounds like your relay is shot. Pull a relay from your fuse box (as close a match as you can get) and substitute your current relay with the one from the fuse box. If the fuse doesn't blow, then you know it's your relay. Had that happen on my friends truck. Starter relay in the fuse box was blown, substitued it with the head lamp relay and we haven't had a problem since.

Note. Be sure to replace the relay you removed.

 

Problem is, I don't think there are any relays in the fuse box with built-in fuses, and I didn't wire a fuse in the power wire because of course the relay already had one. So at the very least I"d have to buy a fuse holder even to test it. At that point I might as well replace the relay as well... Looks like I'll be doing some wiring as soon as the rain stops.

 

I was thinking ground, too. I can see where they're attached to the truck and nothing's loose or looks strange. The relay is grounded with its own mounting screw, and the ground wires from the lights are attached where there was already a factory ground; I just loosened the bolt and stuck the spade connector for the lights under it. Looks like I might have no choice but to crawl around under the truck looking at the wires.

 

I have never heard of a defective relay blowing a fuse. I assume that the fuse is in the load circuit so it sounds to me like you have a short to ground in one of the lights or the wiring going to the lights. Unplug each light and check the resistance at the fuse to ground. It should show an open circuit. If not, you have a short. If you don't have a multimeter, buy one. They are cheap at Radio Shack. Saves tons of time trying to figure this stuff out. If you want more help, PM me.

 

what rattle said. if there's a harbor freight around they sell decent meters cheap. should have one in the truck just in case.

 

I have seen the coil on a relay go bad, but that is not what you are fusing. You are fusing the auxillary contacts weather they be a normally open set or a normally closed set. Both sets of contacts rely on the coil to make or brake them. I would look at the lights themselves if you are blowing fuses. What is the amp rating of the lights? What size fuse is it?

 

Thanks for all the suggestions. I wouldn't normally suspect the relay in blowing a fuse either, but in this case the fuse is built right in to the relay itself. I did a quick visual on the wires and couldn't see any fraying, so I pulled the lights out of the housings just to check and discovered that the one on the passenger's side was shorting.