Both Trailer Turn Signals Blink and Brake Lights Not Working with 2003 Ford F-150  

Question:

Expert Reply:

On a trailer connector in the USA the brake lights and turn signals are combined on the same circuits; one for the left and one for the right. When both of the turn signals blink that indicates that either both circuits are connected to one circuit on the vehicle side or there is a ground problem.

On the vehicle side connector use a circuit tester such as # PTW2993 to determine if the vehicle side functions are correct. You should have 1 circuit for running/taillights, 1 circuit for left turn and brake lights, 1 circuit for right turn and brake lights, and a ground. Sometimes, if the stop light of CHMSL fuse is blown that affects the trailer brake lights. It could also be a tow package fuse that needs to be replaced to get the brake lights on the trailer working.

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 but can show up any time.

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.

expert reply by: Michael H

0