Troubleshooting Trailer Lights Not Working When Head Lights Turn On

Updated 03/27/2021 | Published 03/25/2021

Products Featured in This Question

4-Pole Trailer End Connector

(39)

$7.47

Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(211)

$60.10

Question:

Brake and turn work fine until I turn headlights on then they stop working turn headlights off they work fine 1994 Toyota pickup with new plug and play harness 4 prong flat

asked by: Timothy S

Expert Reply:

Typically when this happens after installing a wiring harness like the Curt # C55379, it's down to one of two causes. You'll want to start by checking the ground connection on the vehicle and trailer wiring harnesses. Make sure that these are connected to a paint, rust and debris free spot on the frame. You'll also want to check for potential shorts on the wiring, where there might be bare wiring touching a metal spot on the vehicle or trailer frame.

The less likely cause would be too many running lights on the trailer, and the harness becoming overloaded. If checking the ground wires as mentioned above, and making sure there is no damaged wiring causing a short does not get your lights back up and running properly, let me know and I can continue to assist you with this issue. I've also linked a helpful article we did on troubleshooting 4 way wiring that you might find helpful as well.

expert reply by: Erik B