I spoke to my contact at Curt and after I explained to him your situation he said the problem is either you are overdrawing the converter box of the # C56049 or are overdrawing the taillight circuits of your 2009 Kia Optima.
His advice was to convert your incandescent trailer lights to LEDs as they draw considerably less which should fix your problem.
I attached a link to the right that has all of the LED trailer lights we offer. view full answer...
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,... view full answer...
First thing to check is to verify that 12 volts are making it to the light assemblies with a circuit tester like part # PTW2993. Next you'll need to make sure the lights are grounding properly. The issue is between either the power or the ground for the lights. Most likely the ground though as that is the more common problem. The part # MCL44AB has a black power wire and a white ground wire. Make sure the connection for both of these is solid. If the ground is an issue you can try running... view full answer...
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