Troubleshooting Right Rear Trailer Light With Running Light Overpowering Brake and Turn

Question:

The R.R. turn signal and brake lights work with no tail lights on. But when I turn my tail lights on it stays lite up like a brake light and turn signal does not work. I have cleaned all grounds down to bare metal. All other lights work. Also its 4pin wiring. Help

asked by: Jacob H

Expert Reply:

It sounds like there is a short within the tail light since this is only an issue on the right rear tail light assembly. If you test the wiring using a circuit tester like # PTW2993 just prior to the tail light, does everything work correctly? If so, then you have an internal issue that could be a bulb, or wiring issue.

However, if you have the same issue when testing the wires prior to the unit, then you are getting too much power from the running light wiring on that side and you have a short somewhere that you will need to trace the wire probing every few feet to find.

I recommend testing the wiring at your 4 way with and then without the headlights on to see if there is a difference on the vehicle side. If not, use a jump wire to connect the functions. If everything works individually, then use a jump wire between the ground connections on either side of your trailer to form a common ground.

expert reply by: Jason S