Troubleshooting Trailer Wiring Issues When Vehicle Headlights Are On

Question:

I bought a new wire harness that goes to my trucks rear wire harness you unplug it a plug eachh end in the trailer harness evrthing works but when I turn on headlights and hit back the trailer lights go out with headlights off evrthing works normally any suggestions please

asked by: Ronald

Expert Reply:

It sounds like there is too much of a draw when your headlights are on and that makes everything else work improperly. There are two possibilities, but it sounds like a bad ground wire versus a bad wiring harness. I recommend checking your ground to make sure it is free of corrosion and rust and has a bare metal to metal connection. One easy way to test this is to take a length of wire and just connect it to your negative battery terminal and then the location of your ground wire on your harness. If everything works with this, then your ground is the issue. Do this with your vehicle first and check function with a circuit tester like # PTW2993. Then connect the trailer and test again using this jumper for the trailer ground. If it works, then you need to improve your trailer ground.

If it doesn't work properly using this method, then I recommend replacing the harness with the T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # 118315 which is a confirmed fit for your vehicle.

expert reply by: Jason S