Troubleshooting Old Horse Trailer Lights Not Working Properly With Different Vehicles

Question:

First our truck lights all work as they should. Next we bought new harness for trailer. So when trailer is connected to truck brake lights work including upper lights along top of trailer. When right turn signal is on, ALL lights flash on the trailer including the left lights. When left turn signal is on, nothing on the trailer works. Now, with truck headlights on and left turn signal is on the trailers left turn signal flashes and the right trailer light is on solid red. Same thing with right turn signal left trailer light flashes, right is on solid but upper right light flashes. If headlights are on and brakes depressed all lights on trailer are lit solid. If hazard lights are on all lights flash on trailer except the right tail light which is on but not flashing. Also we hooked up our Jeep Cherokee to the trailer and got the same senario. HELP.

asked by: Dwaine S

Expert Reply:

Based on what you are describing, and the fact that this happens on both your Jeep and truck, you have a bad ground connection somewhere on the trailer. Make sure all of your ground connections are secure on a clean, bare-metal surface. A bad ground is the only explanation for the bizarre behavior of your trailer lights.

expert reply by: Robin H