Trailer Lights Do Not Work Correctly when Head Lights are On on a 2004 Ford Ranger

Question:

i have a 04 ford ranger and i just got a old 6X10 trailer. i wiried the trailer myself and all went well i thought. anyway my problem is this- with may truck lights on i get all lights good but when i signal left all trailer lights flash and same for right signal, and then when i apply the brakes all lights on the trailer go out, but with my truck lights turned off all the trailer lights work correctly. i have tested the plug on my truck during all light checks and all were good?

asked by: Corey

Expert Reply:

It sounds like you are having a ground issue. A bad ground can cause all sorts of problems just like you are describing. Since you have wired the trailer yourself, it should be easy to locate and fix any ground problems.

Start at the front of the trailer and make sure the main ground is attached to a clean metal surface. If there is any rust or paint you will not get a very good ground connection.

From there, you will need to check the grounds for each of the lights. Most trailer lights ground through the mounting studs if they do not have a ground wire on them. In either case, you will need to make sure the grounds are connected to clean metal surfaces on the trailer frame.

If you added a plastic license plate frame and it attaches to the mounting studs of a tail light, that can also cause a bad ground.

You can also check the wiring for any nicks or breaks because if there is some exposed wiring touching anything metal, that can cause a short.

expert reply by: Michael H