Sounds like it'll want to know the handbrake is engaged - there will be a switch of some sort as there is a dashboard indicator telling you the handbrake is on.
http://www.realoem.com/bmw/showparts.do?model=BT52&mospid=47797&btnr=34_1292&hg=34&fg=30
Part 5 is the switch apparently. This should have a lead you can tap into. However, could you not just 'trick' the headunit into thinking the handbrake is 'always' on? what are the repercussions of doing that?
Hmm that diagram gives me a clue where it will be located. Thanks for helping.
Well I could bypass but I want to fit the unit legally, the unit won't take a simple ground anyway has measures to check it's fitting correctly. It's more so you can't break the law while driving watching dvd's, updating satnav, browsing the web ... lol
Found the cable could access it without taking the carpet out thank god. But the head you says no lol it thinks it's not connected. I defiantly got the correct wire as I could make the dash light go on and off by grounding it