Troubleshooting Trailer Wiring 4-Way Where Running Lights Don't Work

Question:

I bought a C56273 4-pin wiring harness for my 2016 Ford Focus and it worked great after installation. Recently though, my running/taillights do not light up, but the brake and both turn signals work. I checked the wires of the harness and there doesnt appear to be any damage to them. Do you have insight into what could be the cause of this issue?

asked by: Dylan K

Expert Reply:

First thing to try is clean the pins of the 4-way on your Focus and trailer. Most likely it's just a bit of corrosion that needs to be cleaned off that's preventing the circuit from being connected. Typically sandpaper takes care of this the easiest.

To test the converter box you can use a circuit tester like the part # PTW2993 to test for voltage going into the box and coming out with the running lights are on as well.

expert reply by: Jameson C