it seems that the big black plug has round pins, for older C43 radios. the newer ones have the same plug but the pins are flat, as shown on the NOTICE pictures... those pictures in the NOTICE are clearly showing the flat pin radio connector and blue Nav plug and the other one shows the blue and white TV plugs (same deal as nav install).

This unit is not compatible with your car, as your radio is located in the trunk, next to the battery, and this unit should be plugged into the vacated spot for the C43 radio that would have been in place of your nav unit' screen.

I guess, it is too late now, as the wires probably were chopped - but the installer should have known better than this and should have advised you accordingly before taking a knife to the patient...

theoretically, if you can locate the iBus wire in the new radio and connect it to the iBus in the car, you can gain the steering wheel controls but with the system being rigged like that, it is just a wild guess...

good luck