The Quadlock cable is the interface to the car.

I had mine professionally installed and have a 4m extension cable that runs from the BMW adapter to to the rear, and then connects into the Quadlock cable and connectors somewhere by the battery. You can't simply connect into the CD multichanger (as I'd also hoped you could).

I have the Pro Nav kit, plus Pro Bluetooth phone. The installer had to remove the spare wheel, air suspension compressor and several other bits to get access to the relevant modules by the battery. He then had to change various wires in the OEM Quadlock plug to allow connection and correct functionality. I'm sorry to say that having seen what needed to be done I was happy to pay someone £50-00 for the two hours it took him to finish it.

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Me:
Current: 2011 E71 40D Vermilion Red/Beige Nappa

Wifey:
Current: 2012 R80 Countryman SDX Green/Cream