Troubleshooting Trailer Lights Not Working After Installation of 4-Pole to 7-Way Wiring Adapter

Question:

My connectors were old and worn. I was towing a and it worked fine when I disconnected the lights the connectors felt very hot the next day I tried to reconnect them and nothing happened so I bought a new wire harness and changeed four prong four prong into the circle seven thingamajig . Anyhow I plug it back in and I have no lights I checked my fuses and they are good

asked by: Sean A

Helpful Expert Reply:

If your trailer connectors became hot to the touch there is a chance that a fault somewhere in the trailer or vehicle wiring has caused damage to the harness. Severe corrosion on your connectors or a short somewhere in the trailer wiring could lead to an overloaded/damaged harness. Since you already replaced your vehicle's 4-pole harness with a new one, like the Tow Ready # 118376 that fits various Chrysler vehicles, and since your vehicle fuses are okay, I suggest you test the 4-pole by itself first before connecting a 4-pole to 7-way adapter.

You can disconnect the trailer and test the vehicle 4-pole's pins for proper signals using a circuit tester like # PTW2993. Have a helper activate each lighting function one at a time while you apply the grounded tester to the pins. Please refer to the linked photo which shows you which pins carry what light functions. Vehicle headlights should activate the brown wire and brakes and turn signals should activate the yellow and green wires. If you find these signals on your 4-pole then you can move on to the 4-to-7-way adapter you're using, an item like # 37185 it sounds like. Test the contacts on the adapter in the same way to see if the signals going in on the 4-pole are coming out at the 7-way socket. If not the adapter may be bad.

If you do NOT find the correct signals on the vehicle's 4-pole harness and all of your fuses are okay, then you may have a damaged harness. Check the trailer carefully for any signs of worn or cracked insulation that could have caused a short. Unless found and fixed a short on the trailer could damage a new harness so you'll want to make sure the trailer wiring is okay before installing a new harness.

expert reply by: Adam R