Trailer Brake Lights/Turn Signals Do Not Work After Installing Wiring Harness on 1984 Toyota Pickup

Question:

I have a 1984 toyota pickup. I bought a four way trailer plug. It has 2 turn wires a brake light wire, running light wire, and a ground to attach to my truck that goes to a box then to a four way plug. I have plug tester to plug into my truck 4 way. I did and it shows everything works. When I hook up my trailer. Only the running lights work. Please help

asked by: Brent

Expert Reply:

Since you have tested and everything works on the vehicle side the issue must be on the trailer side. But to be sure make sure the harness you installed is properly grounded to a clean and corrosion free bare metal surface and that all the fuses related to the tail lights are good.

On the trailer, first make sure the trailer connector is clean and the pins do not have any corrosion on/in them. Then make sure the main trailer connector ground is attached to a clean and corrosion free bare metal surface.

Check the grounds for the lights as they too should be connected to a clean and corrosion free bare metal surface. Many lights ground through there mounting studs so keep that in mind when checking grounds.

Then you can check the wiring to the lights. Since it is the turn signals and brake lights not working (they share the same wires, 1 per side) check that wiring from the connector to the lights. Check for breaks in the wiring or loose connections.

If the trailer has an aluminum frame, tilt bed, or folding tongue then running jumper grounds from the lights to the main trailer connector ground can help. I have included a link to an FAQ article that should help.

expert reply by: Michael H