im in the same boat as you jjdryer. i purchased a snugtop off of craigslist about a month ago and still have not hooked up my cabin light or 3rd brake light. The snugtop came with a harness on it and ive been look for the same kind but have been having no luck.
im thinking about jus going to autozone and getting a new one but i would kinda like it to be how it came.
If you have the tow pakage on your truck. Not just the four way flat wire, but the factory towing package with the 7 pin connector you can run a wire and splice it into the 12volt wire that is in the wiring loom for the tow connector. I am not sure what color wire off the top of my head. Doing it this way will make sure that you never have a dead battery because the light was left on becasue there is only power to the tow package if the truck is on.