Bought this off Amazon for $45 delivered.
Bought a cool rear hatch light off Amazon. It arrived with zero instructions at all. Like, nothing, nada, zero. So I popped off the little panel on the rear cover where it goes and look around. Not evident where it plugs in. Search around and find a youtube video showing how to remove all the panels and where the harness plug is. Friend and I pop off the panels, which is super easy, then spend probably 10 minutes searching for the harness. Finally do, it's this one here, on the right hand side if you're facing away from the truck. You need to pop off the clip holding it to the metal hatch
Run the wiring behind all the metal and plug it in.
Put all the panels back on. While snapping in one of the side panels, realize that you were dumb and didn't take the plastic retainers off the body and put them back onto the trim. Argh! Shake the hatch so they fall to the bottom, then remove the inside tail light to find them. Little bastards, there you are!
Carefully inspect all the trim panels to make sure all the clips are on them, remove another clip off the back of the metal hatch and put it on the trim. Snap the trim back into place and struggle to plug in the 3rd brake light. Finally done! Push the button and nothing happens. Hmmm? Ask on 200 FB group, turns out it has an internal battery and you have to run the rear wiper some to charge it. Do that and success!