None of the wires on the curt 4 pin setup. The backup light wire will require a fifth wire tapped into the hot wire that runs to the backup light power of the truck. If you want backup lights on a trailer using Curts 4 pin setup you can add a 4 pin to 5 pin adapter with the separate backup light wire to the fifth wire in that plug. Also if you have a trailer with surge brakes you can use the 5th wire as a cut out for when you want to turn off surge brakes. But if you want both you will need six wire connections. I would just call curt and tell them what you want as they may have other tplugs not shown on web site. Check but I believe Curts 4pin limits running lights to 3-4 amps Per side of trailer. This looks like the 12v bed circuit should handle the load if it's active at the times you need it to be.This is the Curt harness. So one of these white wires? If so, how do you determine which one is for reverse (which one to splice in to)? Is there a wire schematic available? Thanks
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