Troubleshooting Trailer Wiring Harness on 2009 Kia Optima

Question:

curt harness for 2009 Kia optima shows everything is working when put on tester, but when hooked to a known working trailer, trailer lights do not work. I have put on two harnesses with the same results. Even added extra ground thinking this would help. All this work was done at a local service center and they are stumped. they called company rep but all he said was we have not had any issues. Do you have any ideas?

asked by: Gordon J

Expert Reply:

What kind of tester are you using? I'd use an incandescent bulb tester like part # PTW2993 on the vehicle trailer connector while each function is activated. Turn on right turn signal, test pin fed by green wire. Turn on left turn signal, test pin fed by yellow wire. Turn on running lamps, test pin fed by brown wire. Applying the brakes should cause the pins fed by the yellow and green wire to show voltage.

If you're showing power on the appropriate pins as each function is activated, I'd be inclined to believe the problem is in the trailer wiring.

Try plugging the trailer into the vehicle, and then running a jumper wire from the grounding point on the trailer tongue to the negative battery terminal on the vehicle. If this causes the lights to function, it indicates that there's a poor ground on the trailer. Make sure the ground on the trailer tongue is securely made to clean, non-corroded metal. Each lamp should ground either by a ground wire connected to the trailer frame, or by its mounting studs being in direct contact with the trailer frame. Make sure each lamp is properly grounded.

Have you tried your trailer on another vehicle? This would further help narrow down if the problem is in the trailer wiring or in the vehicle. You could also try the Tow Ready harness as an alternative, it's part # 118433.

I'll also link you to our trailer wiring troubleshooting guide, I hope you'll find it helpful.

expert reply by: Mike L