Troubleshooting Ground Problem on Trailer Towed by 2004 Nissan Frontier

Question:

Check my flat 4 connector with a probe lights up fine with right and left headlights brake lights all seem good with the probe. Plug into trailer lights and very faint but both lights blink at the same time. Headlights on nothing. What I found was power coming through the white ground wire. It would barely light the probe but when I had the blinkers on it would blink through the ground wire along with the correct wire. Took the ground wire off sanded the area and cleaned it still the same thing. Any ideas?

asked by: Kerry M

Expert Reply:

If the main ground has been improved and you're still having the same problem, check the points where the taillights themselves ground. This is a pretty common problem. Things work well (or fairly well, in your case) until the running lamp circuit on the trailer is turned on. At that point, the lighting is pulling the maximum amperage and that's where a ground problem will show itself.

Each lamp should either be grounded via a separate ground wire to the trailer frame or by it's mounting hardware being in direct contact with the trailer frame. Check and clean those grounds like you did up front, and you should be good to go.

One last thing, sometimes the design of the trailer itself can cause a ground problem. If the trailer has a tilting bed, or a swinging or tilting tongue over time the pins in the hinges can wear causing ground problems. If your trailer is designed like that, simply take a length of wire long enough to join the stationary and the moving part of the trailer, install a ring terminal on each end and tie the two parts of the trailer together, which will solve the problem.

I've linked to some trailer troubleshooting articles that you might find helpful.

expert reply by: Mike L