Grounding on Trailer Shorting Out Vehicle

I bought a fixer-up utility trailer a few months ago (dirt cheap, which is why I bought in instead of a ready-to-go one). The wiring needed to be redone, and additionally there was no license plate light. I have bought and installed a couple, but now when I try to ground them, they short out. I've even tried grounding only one at a time, but it just does the same time. It blows a fuse on my vehicle, disabling the tail lights. I bought a pack of replacement fuses so that I can still drive my car.

I have tried grounding the license plate light in three places on the trailer - by each of the rear tail lights, and in the very front of the trailer next to the main ground wire. They all blow the fuse, no matter where I attach the ground. Right now, the grounds for both of the license plate lights are unattached.

Everything else on the trailer works without any issues.

If it's worth mentioning, my vehicle has independent turn signals and tail lights, whereas the trailer uses the same bulb for both. I bought a converter kit for the vehicle though, so that shouldn't be a problem.

http://i.imgur.com/5pAesIM.png

If the fuse blows when the grounds are connected, it has nothing to do with where you are connecting the grounds, it has to do with how you have the lights wired. It sounds like you have the bulb ground and one of the power wires reversed. The bulbs in your trailer have two filaments and, if they are 1157 or 2057 bulbs, two little bumps on the socket end. Each of those bumps go to one of the filaments, and both filaments are tied to the common metal base of the bulb. Somewhere it sounds like you have one of the wires for one of those "bumps" wired to ground. The parking lights work with the ground disconnected because the bulb is getting the ground through the second filament and the miswired connection that is currently shorted to ground.

If you are not willing to take the time with a continuity tester or a multimeter to figure out which bulb it is, buy a bunch of fuses, then pull all the bulbs, connect all of the grounds at all of the sockets, plug the trailer in with the lights on, then install bulbs one at a time until the fuse blows. Figure out the issue at that socket, then continue to the rest to see if it's only an issue with the one socket or multiple sockets.

-Rod

I'm with Rod on this one. You have something wired incorrectly. The only way grounding a wire would cause a fuse to blow is if that wire was powered. You don't even need a multimeter really, a test light would help track your issue.

Any of your lights LEDs? Those are polarity sensitive......

That wouldn't affect the fuse blowing though. People misinstall LEDs all the time and all that happens is the bulb doesn't work or is extremely dim.

It turned out that the lightbulb was broken. I must have damaged it by accident, because it was brand new. Once I bought a replacement, everything worked.

Glad to hear you got it figured out. Thank you for following up with what you discovered.

-Rod