I know for a fact that trailer lights are finicky. In this case, is the ground through the trailer ball or is there a ground wire? If it's through the ball, all kinds of problems can occur, including sporadic lights. Wires get loose. If a trailer has been in the water, temporary shorts can occur. The light plug to the pickup can wiggle around and temporarily not connect. Occasionally, but not often, the plug itself will go bad and need to be replaced. I've pulled trailers for 40 years and I've seen them all. I'm having a problem right now with the light plug on my pickup. The taillights seem to be on or off at will. I've checked every connection in the thing and found nothing wrong. Often, the best fix is to just rewire that circuit and be done with it and that's what I plan to do.
Don't blame the cop until you have proof that the lights were working ALL the time because in all likelyhood, they were not.
Dick
