Wiring Aux Backup Lamps

[Green_Manalishi]

2017 2500 adding backup lamps and I want to tap into the trailer wiring loom. What I read was YEL is for reverse, WHI is the ground. Well, when I wired it up, that wasn't the case, and I don't want to tap/strip all the wires in the loom. Yes, the lamps work when I touch the center (Rev) and lower right (Gnd) terminals on the plug from the front, but I can't see which wires they are from the back.

Anyone know, on a 17 2500, which is which?

Thanks.

 

[diymirage]

Shoot. That is how i wired mine up, but i just pulled the trialer plug out (disconnected it) and tapped right into the wires

Cant remember the colors though
I just popped the whole thing out of the bumper and traced it back that way

 

[62Blazer]

I believe the truck should have a separate reverse power wire already running to the back. So no need to tap into the trailer harness. I have a '16 that had that extra wire in the harness in the back passenger side, near the spare tire, that just ended and was taped off from the factory. It provides 12 volt power when in reverse. From my understanding this is standard on that generation of 2500 from the factory and was offered for items like back up alarms and such (the back up alarm is a factory option in these trucks). Just connected to that wire and grounded the lights to the frame.