Ok here is the situation. I hooked up my trailer lights to find that the running lightson the trailer dont work when I turn the truck (2001 GMCSierra)lights on. Everything else worked. Found the bad wire on trailer harness and fixed it. Now when I turn the truck lights on, the rightrear light is out,but the brake light works. The left rear light is fine.Any suggestions?????

 

Use a test light to check the trailer and the harness.

 

Checked harness with the light and found that there seems to be a problem coming from the panel. I pulled off theplug that supplies the power to the rear lights, and with the lights on, I tested and got only one slot to light up. Guessing that its the power for the light that works. Does anyone knowif there is a fuse for each tail light?

 

I wouldn't think there is Id say they are on one fuse. I think the brake lights are on a different fuse. Dose the Bracke lights both work? And did you test it were the light bulb plugs in? That might be a good place to start. Test it there if there isnt power go to the next closest place you can test it and so on. Work your way to the truck or find the last place you get power and that is were the problem should be.

 

Yep. Cracked wire right past the spare tire. Looks like a rock or something poked a very tiny hole in the insulation. Just a small spot of corrosion. Touched the wire and it broke. I must havebroken it while messing with the trailer lights.