I currently rewired my race car trailer. All lights are now led. The problem is when the trucks plugged in I have running lights but the turn signals and brake lights do not function correctly. The turn signal barely flashes and when the brakes are applied it makes all trailer lights flash with the turn signal pulse. Plugged another truck into the trailer and everything works flawlessly. Plug my truck into a 2020 trailer with all led lights and my truck operates that trailer correctly. But for the life of me my truck and trailer will not cooperate. I put a voltage meter on the trailer for the turn signals and brakes and with the other truck it would read 12v. With my truck it reads under a volt. My truck plugged into the new trailer registers 12v as it should be. Any idea so what it could be?

 

Start by cleaning and greasing the 7-pin under the weather cover. Then crawl under the bumper, disconnect the connector on the backside of the 7-pin, and clean and grease that as well. Then find the connector a little bit down the harness, clean and grease that as well. While you're under there, do the same for the ground connection at the frame.