[Brent]

The first thing I would do is make sure the ground wire (white) of the wiring harness on the trailer is securly attached to the trailer frame and that the mounting bolts for the lights are grounded to the trailer frame as well. For the wiring harness ground I like to use an eylet and a drill point (self tapping) screw and attach it to the trailer tongue. Never depend on the hitch for a ground. Why? When you apply the brakes on the truck the trailer pushes forward slightly and the front of the coupler does not make good contact with the ball, and the rear portion of the coupler is usually dirty/rusty/grease covered and does not provide a good ground. During the day when the tail lights are not on, the current from the brake lights will backfeed through the tail lights thus the tail lights on the trailer light and appear as dim brake lights. This is bad enough, but it gets worse, at night when the tail lights are on and you apply the brakes, the ground is lost again, but now the current cannot backfeed though the tail lights because they are powered and the tail lights which were working because they were using the brake light filaments as a path to ground now go out thus resulting in the stopping trailer having absolutely NO LIGHTS.

Before trouble shooting trailer lights, always make sure the ground wire on both the vehicle and trailer harnesses are grounded to the frame then proceed to troubleshoot the lights with the trailer not touching the tow vehicle.

If this doesn't fix your problem let me know and I can tell you how to test the truck and the trailer to isolate the problem.

Good luck,