I've been hauling around big rig trailers for over 25 years. For 10 of those years I might hook up to as many as 10 diferent trailers a day. The #1 problem I've seen in trailer lights was a bad ground. I made up a 25' long piece of 10 gague wire with spring clamps on each end. The type you might see on some small battery chargers. I'd use this to make sure I had a good ground if I had light problems. This gets rid of one possiblity in the chain and if it doesn't solve the problem you go on from there. By using a jumper like that hook it the ground from each light and see if any of they aren't grounding right. If you have a ground problem it will try and ground its self thru the other side of the lamp. Thats why you'll see all the marker lights flashing sometime on a trailer when the turn signals are on. The turn signals are grounding thru the marker light ciruit. I'm just trying to help here.bigdude said:
70~K5- I put a new ground in the harness to the trailer. I followed all wires (and checked their connections) through to the ground on the tow rig. I didn't see any issue.