I want to say it switches (power) to the reverse lights. All those lights are grounded back at the tail lights. I put a new complete wiring harness in the truck, so I can only say my wires are white, going and coming from that switch.
You could probably find the fuse for the tail lights and tap into that, run the wire into the switch and another wire from that switch to the reverse lights.
Sorry, I don't remember what the color wires are for the neutral switch. I'm about 99.99% sure I'm not running them. (It's been a while since I re-wired the truck and it's raining outside)