I read on several forums that there is supposed to be a trailer brake controller that plugs into the wiring harness under the dashboard on the drivers side, but I can't find any Part Numbers or if the thing is plug and play. I do plan on towing with it up to it's max, and I'd like there to be a controller I don't have to manually wire in.

I do have the harness I believe what I spotted when I had the dash apart taking care of another issue..

Where could I find this controller?

My cayenne does have the factory towing prep package, so the receiver is there and so is the 7-pin connector. The towing system has never been used, the receiver shows no signs of anything being attaches. zero rust or chipped paint.