Re: trailer lights
Dim relative to what? Why not determine first if they are working normally. Start with the connections and particularly the ground (white wire) on the tow vehicle. If that checks out ok then move to the trailer. Good ground on white wire. Good ground at each light. If you have a pivoting/tilt trailer there needs to be a ground strap across the pivot points. Remember, the frame is being used as a wire so any joints are potential points for ground issues.
