Yes, it mounts permanently to the tongue of the trailer. You plug the Prodigy RF controller into the truck’s 7 blade receiver, then plug the trailer’s electric line directly into the controller. You regulate the +/- gain and hand brake feature with a remote control that plugs into the cigarette lighter.
It works exactly the same way as an under-the dash brake controller would work, with proportional control of the trailer’s brakes through the electric line. But nothing is hard-wired or installed in the tow vehicle. It was designed for situations where a trailer might be towed by multiple vehicles, or you couldn’t install a controller in the vehicle for whatever reason. And it was a life saver when I was constantly borrowing and renting trucks while mine was on the fritz.
My new truck has a factory in-dash controller, so I don’t use the Prodigy RF anymore. But I still have it on my trailer just in case.