Troubleshooting Trailer Lights Going Out When the Brakes are Applied After Trailer Light Kit Install

Question:

Wired up an Optronics 4-wire system on trailer. All lights come on at startup, then Any turn signal flashes BOTH trailer lights and when I hit the brakes the lights go off. What might I have done? Appreciate any help.

asked by: chris r

Expert Reply:

It sounds like you have a ground issue. When trailer lighting does not have a sufficient ground many different scenarios can show up, but the most prevalent is when the most amperage is applied, like tail lights on and brake pedal pressed, the lights go out. All lights must be properly grounded for proper function.

When installing the standard trailer light kit, # TL29BK, the lights are grounded through the mounting studs. You need to make sure that the mounting studs are contacting the trailer frame and that no paint or corrosion is impeding the ground connection. The plastic license plate bracket can also contribute to a ground issue.

If you have attached any of the lights to wood or other area that is not grounded, you will need to run a jumper wire from the mounting stud that grounds the light to the trailer frame for each light.

You also need to make sure the white wire at the trailer coupler is attached to the trailer frame and that the attachment point is free of paint and corrosion.

I linked a installation video that shows how to install the trailer light kit and explains the ground connections for the lights.

expert reply by: Robert G