Troubleshooting a Trailer that Blows Vehicle Tail Light Fuses and Sparks When Touched to Hitch Ball

Question:

I have a 1998 Chevy S10 pickup and a 5x8 tilt trailer of unknown vintage. When I acquired the trailer the lights were trashed so I replaced the lights and ran all new wiring. Heres my conundrum...if I hook the trailer up to the hitch and plug in the lights the fuse for the right rear tail light on the truck blows. The brake lights and turn signals on the truck work and all of the trailer lights work. If I remove the trailer from the hitch but leave the lights plugged in and replace my blown fuse the truck lights all work, the trailers tail lights and turn signals work, but when I apply the brakes the trailer lights go out. Also if I rub the trailer hitch against the ball I will sometimes get a spark. I have checked the trailer wires for exposed areas and found none and I cleaned all the grounds on the trailer. My assumption is there must be a short somewhere, I just cant figure out why all the trailer lights work but the trucks tail light fuse is blown.

asked by: Kevin R

Expert Reply:

It sounds like there is a 12 volt short on your trailer. The spark you are seeing is because your trailer frame has 12 volts running through it and its grounding to the ball and sparking.

It sounds like its the running light circuit since that would most likely be the circuit that would be left on if you were hitching or unhitching a trailer. This would also explain why your tail light fuse is blowing. You should go over the running light circuit very carefully and see if there is any exposed wire touching the frame of the trailer and fix as necessary.

I attached an FAQ on trailer wiring for you to check out also.

expert reply by: Jameson C