We had this
Prodigy one on our last TT. The control unit mounted on the TT frame and plugged into our truck. The TT cable plugged into it. Really handy when pulling with multiple trucks ...and my knees weren’t constantly hitting it.
You did not actually “need” anything in the truck for it to work. But it came with a remote control that plugged into the cigarette letter for a display, setup, and a manual control. I hung mine from the air vent right by the shift lever where you could see it and access the manual switch easily. It did pair with the unit on the TT but I’m not sure if it was Bluetooth or not.
It was the best, easiest to use brake controller that I ever used.