Hello,
I have a 2001 Dodge Ram 2500 that I recently bought a snugtop canopy for. There's a harness on the left side near the tail light. I have absolutely no idea how to wire things properly. Is there a plain english, step by step guide on how to do this somewhere? I would greatly appreciate the help.

 

Dark green wire with brown stripe is your brake lights. Of course, if you wire it to one side, it will blink with that turn signal as well.

 

I saw someone somewhere mention that there's an adapter for that? So what is the significance of the 3rd brake light wire that "may or may not exist" near the spare tire?
Thanks!

 

The third brake light get the feed direct from the brake switch. If you have the trailer package you could use the wiring from that. If not you have run a wire back from the brake switch if you don't want it to flash with the turn signals.