Isolating Wiring Ground Problem to Vehicle or Trailer

Question:

None of my trailer lights are working... but slightly lighting up when braking and flashing. When braking, the radio lights turns off, when flashing, radio blinks so it seems to be a ground issue. Running lights not working at all and when braking I get so little lights, but from all trailer lights. Tracked down a ground problem, heres where I am now... Spliced ground at the car/trailer connection with a jumper wire and connected it to a car ground : no result Spliced ground at the car/trailer connection with a jumper wire and connected it to trailer frame : everything seems to work fine. What to do now, is the car or the trailer the problem in this case ? thanks

asked by: Steeven

Expert Reply:

Ultimately all grounds on your trailer are referenced to the tow vehicle's battery negative terminal. The main trailer ground pin on your trailer's plug connects to the vehicle socket ground pin and that wire then runs to the vehicle frame, where the battery is also grounded. So in the end all things ground to the vehicle battery negative terminal one way or another.

You could have a ground issue on the trailer, vehicle or both. It is easy to test to find out. Simply disconnect the trailer from the vehicle so that you can test the trailer on its own.

Connect the vehicle battery's NEG terminal to the ground pin on the trailer plug; then connect the battery POS terminal to each one of the other pins on the trailer plug, one at a time, to see if each of those lighting circuits operates properly when directly powered in this fashion. If they all work then you know the ground issue is on the vehicle. If they do not work then you need to check your main trailer ground to ensure that wire is solidly attached to a clean bare metal surface on the trailer, one that is free of paint, primer, rust, grease, etc. You need a bare metal to bare metal connection.

If you have an issue on the vehicle side again make sure the main trailer socket ground is solid and made to clean bare metal.

Once you get it all sorted out you can protect the new ground connections using dielectric grease # 11755. This will block water and dirt from the ground connections and keep them functioning longer.

expert reply by: Adam R