Has anyone had a dealer successfully install the OEM brake controller, wiring harness and hitch receiver on a 2011 X5?

The dealer can't get the installation to work properly on my 2011 35d. They've been working on it since early summer. It's been a brutal process.

Everything appears to be working now except the circuit that allows the car to charge the trailer battery. Anyone have any ideas on how to fix this?

Thanks.