Troubleshooting Trailer Wiring on 2009 Kia Optima that Stops Working When Plugged into Trailer  

Wondering if anyone has had success installing a Curt C56049 wire harness on a 2009 Kia Optima. Have done everything all the experts have recommended but have had the same problem I see a number of others have complained about. Everything works fine before the trailer is hooked up. Hook up any trailer and the turn signals and brakes dont work right on the trailer. The presence of a trailer screws up something in the five-to-four wire box. Unplugging the trailer seems to reset the box and the tester once again gets good signals on all wires all the way to the plug. Hook up the trailer and things go haywire again. Have a great ground from the trailer to the car, so that is not the problem. Have hooked up several other trailers all of which work fine with other vehicles and none of which work right on the Kia with the Curt harness. Have noticed some voltage bleeding likely because of the extremely thin ground wires used in/around the connectors for the Kia brakes and turn signals. Even had an electrical engineer splice some diodes into the wiring harness to the voltage a bit hoping that this would keep the box from receiving a false feedback signal. Tried a second harness. Nothing has worked. Please let me know if you have gotten a C56049 to work or if there is a harness from another manufacturer that works on a 2009 KIA Optima. I think you can understand my desire to know that there is some possibility of success before wasting more of my money and time. Thanks in advance for any help you can give me.

asked by: John V