Toubleshooting Trailer Lights Not Working When Brake Pedal is Pressed

Question:

I have a 2005 GMC and when I plug my trailer in I have lights until I press my brakes and then I lose all lights on my trailer. What am I doing wrong or what is wrong?

asked by: Robin

Expert Reply:

It sounds like you have a ground issue. You can use a circuit tester, like # PTW2993, to determine if the issues is on your vehicle or on the trailer.

Using a circuit tester, you can test the pins on your vehicle connector to ensure they are all working properly. Another option is to hook the trailer up to another vehicle with properly functioning wiring to see if the trailer lights work properly. If the trailer lights work with a different vehicle or the circuit tester shows your vehicle end connector isn't working, the issue is on the vehicle.

If the vehicle end connector has a ground near the connector, you will want to ensure that the ground location is clear of rust, corrosion, and debris. If the vehicle has factory tow wiring, you can take the vehicle to your local GMC dealer to have the wiring checked out.

If the wiring on the vehicle is working properly, then the ground issue is with the trailer. If your lights are grounded to the trailer, you will want to be sure the ground is clean and free of rust, corrosion, and debris. It is best to locate the ground to the trailer frame where the metal is doubled. It is a good idea to run all of the light grounds back to the main trailer ground if possible.

expert reply by: Victoria B