Can't Nat, How temporary will the four pin connection from the car side be? Just to get a trailer home? That you have a 7 pin connection on a trailer implies it has electric brakes, implying it is heavy enough to warrant having brakes. That added trailer momentum without dedicated brakes may further reduce the car's ability to safely slow and stop the combined rig. The four pin connection on the car won't supply the electrical power to the trailer's electric brakes, regardless of adaptation. You'll need to add a controller (to apply a proportional amount of current to the trailer brakes), wiring from that controller to the trailer's brake circuit in the trailer's 7 pin plug, and possibly wiring from the car's 12 volt circuitry to the brake controller (some are pre-wired to that point, our Audi was, our prior VW wasn't). I'm personally partial to hydraulic trailer brakes for the simplicity and lack of additional tow vehicle modifications, but the trailer manufacturer made a choice, we wanted that model, and it was less trouble to add the needed circuits to the t-v than to change the trailer.