Troubleshooting Tow Ready Wiring Harness, # 118552 on a 2008 Dodge Grand Caravan

Question:

Installed #118446 on 08 Dodge Grand Caravan last summer and they lights on my trailer lit up no problem. Went to try this summer and left brake light stays on. Checked all the wires leading into the modulite and they all work as they are supposed to, but all that comes out properlyare the blinkers. Yellow wire has power at the trailer connector all the time. Could this mean there is a short where the light stays on, or is the modulite garbage? All helights on the trailer are working. Problem is without trailer connected. Thanks

asked by: Derrick

Expert Reply:

If a signal is going into the Tow Ready Wiring Harness, part # 118552, Modulite box and not coming out, or a signal is going into the box and coming out on the wrong wires the ground on the vehicle may not be connected properly. If the white ground wire is not installed properly on the vehicle, then the green and yellow wires will not carry signal coming out of the box.

To check the ground wire on the Modulite box you will want to use a circuit tester like part # PTW2993. First, connect the circuit tester's ground wire to the same location as the ground wire on the wiring harness. Then test the signal going into the Modulite box. If there is no signal, connect the circuit tester to another grounding location such as the exhaust pipe. If a signal is present, the grounding location for the wiring harness is bad, and a new location needs to be found. Do not utilize the tailpipe as a permanent ground location.

If the ground is good on the Modulite box, then the Modulite box has shorted and would need to be replaced.

Usually if a wiring harness works properly when installed, then goes bad, it is most likely from a short with the trailer wiring. You will want to make sure and check the wiring on your trailer for a broken, pinched, or frayed wire that might be making contact with the trailer frame or another wire in the harness.

I am including a link to a FAQ page on trailer wiring that will describe how to troubleshoot your wiring harness.

expert reply by: Jeff D