At that point, it’s probably time to just yank that whole wire harness going to rear and make up a nice pretty new one

 

Not an overly complex harness.

 

So a little bit of a win. I'm guessing that after my friend ripped out all of this prior owner's make-shift harness for the Dolley he accidentally plugged or got some debris in the rear harness connector for the driver side. I thought it was weird that it wasn't working because when checking them with my multi-meter each connector had enough power going to them besides the driver reverse which has a lot less. I'm guessing there's either a break in the harness somewhere or that wire is just shot. Either way, the driver-side brake, reverse, and running light work so that's a win.