Troubleshooting Curt T-Connector Wiring Harness # 56010 with Left Blinker Always On

Question:

I installed a curt t connector, it worked fine for about two months now the left blinker light stays on. I checked the trailer with a battery and all the lights work just fine. I checked the connection at the car with a multimeter and found the problem. The plug to the left blinker has a constant 12v running to it, with the blinker on or off. Just wondering where I should start to fix this problem. Any help you can give is appreciated.

asked by: Neil

Expert Reply:

Thank you for clearly describing the issue you are having with your Curt T-Connector trailer wiring harness # 56010 and also the troubleshooting steps you have taken to diagnose the issue in your Mazda MPV van.

Apply your circuit tester (such as # PTW2992; see linked video) to the yellow wire leading from the left T-connector to the left (input) side of the converter box. This is the wire that carries the left turn signal from the vehicle to the harness. If this wire carries a 12V signal without the turn signal engaged, then the problem is within the vehicle wiring upstream of the harness.

If the yellow input wire carries a signal only when the blinker is on (this is what you should find) then move on to test the yellow wire that leads from the right (output) side of the converter box to the 4-pole trailer connector. If this output wire carries 12V all the time but the input side behaved properly, then this indicates the harness is damaged and needs to be replaced.

expert reply by: Adam R