Why Would Trailer Taillights Only Work When Trailer Coupler Is Touching Ball Mount

Question:

I have a 2011 Chrysler Town and Country Limited. I purchased the Curt Class III tow bar Item #13364, a T-One Vehicle Wiring Harness with 4-Pole Flat Trailer Connector Item #118534, and a Hopkins Adapter 4-Pole to 7-Pole and 4-Pole Item #37185. I installed everything and hooked up just lights from the trailer and no lights on the trailer worked. I grabbed a tester and everything works fine. I then coupled the trailer to the hitch and hooked it up and everything worked fine. So Im assuming I dont have a sufficient ground. I grounded both item #118534 and #37185 to the vehicle frame and also ran the power wire to the positive terminal on the battery from item #118534. I realize Ill never pull the trailer without it being coupled and it is a utility trailer that will never need 12V power. Im just curious as to what is going on. Is the ground wire supplied with item #118534 and #37185 not sufficient? Im not very mechanically inclined but Im pretty sure coupling the trailer to the hitch should not be necessary to ground the vehicle trailer wiring. Any help would be very appreciated. Thanks.

asked by: Paul C

Expert Reply:

It sounds like your trailer wiring is grounding through the coupler, to the ball mount, and then to the hitch and frame of your vehicle. This is a pretty common occurrence as a lot of trailer wiring setups aren't grounded sufficiently. It would be a good idea for you to run jumper wires from each of the light assemblies on your trailer to the main ground of your trailer.

Since couplers move around a bit on hitch balls your current setup might cause erratic light operation if the grounds aren't improved.

expert reply by: Jameson C