Actually, it sounds like there is a bad ground. Check and make sure the ground on the vehicle is good and clean. Also, with a test light, make sure you have the correct wire from the vehicle going to the correct wire on the trailer. If you are not sure of the wire on the trailer, use a battery charger to supply power to each pin until you find the correct one for the brakes. As far as a relay, I wired a lot of trailers over the years (infact I have an Expedition in my driveway that is wired for a camper and a small trailer) and never had a brake light relay, whatever that is.
Let me know what you find.
Tuesday, November 10th, 2009 AT 8:04 PM