Colan

2020 Duramax 3500 Using a Curt adapter for LED lights on new 5th wheel, all but the left turn signal is working. Trailer turn signal wiring checks out, connected to another power source, through the trailer seven pin cord everything works. With the adapter and the right turn signal on, with a volt meter you can see voltage bounce between 12 and zero as expected. Left turn signal on, nothing. Here is where it gets really weird. Plug the Curt adapter into the seven pin receptacle on the bumper. Plug the trailer 7 pin connector into the receptacle in the bed. Everything works as expected.