Trailer Lights Go Out when Vehicle Brake Pedal Is Applied and Both Turn Signals Blink

Updated 09/11/2014 | Published 09/10/2014

Question:

Lights turns on but when brakes are apply trailer lights dont work. When signal either left or right both trailer lights react as it was a hazard light. Boat Trailer has been tested on another vehicle and it works fine....Im stuck now see if you can give me some tips to narrow the problem

asked by: L

Expert Reply:

This sounds like a ground problem. The first thing you should know is that testing the trailer with another vehicle is not a fool-proof way of determining wiring issues on the trailer. The other vehicle may have a wiring system that can overcome the ground problems that the intended vehicle cannot.

Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

You can also test the vehicle side trailer connector without the trailer connected using a circuit tester such as # PTW2993. I have linked a help article to the right that should help you troubleshoot.

expert reply by: Michael H