Brake Lights Not Working With Trailer Wiring Harness # 118242 Installed on a 1999 Ford F-150

Question:

what is happening! Replace swith fuses bulbs and 4 pin trailer plug. No brake light to rear bulbs but dome brake with 912 works. There also a hot brake wire that not used where to hook it into!

asked by: David S

Expert Reply:

As you have found, where the connection point is for Trailer Wiring Harness, # 118242, there are more wires going in then coming out of the factory connection point. This requires a little bit of hardwiring. There should be a blue and orange wire on the truck behind the forward plug.

The blue wire on the truck would go to the blue wire on the wiring harness. The orange wire should connect to the black wire. The cab or dome brake light working sounds like it is connected to the CHMSL circuit but not the rear tail lights. The hot brake wire you mention might be the correct one, unless it is hot all the time. If it is hot all the time (brakes applied or not) then it is the 12 volt power wire from the front of the vehicle.

It sounds like there are just a couple of connections that need to be switched and it will work like it should. I have included links to a video installation of the harness, the installation details for reference, and an FAQ article that should help.

expert reply by: Michael H