BTW, all this talk of CAN bus etc. got me interested enough to learn more about the buses in the E53 and as usual, Qsilver7 comes to the rescue.
Turns out there IS some CAN bus in the E53 but it's restricted to DME/DDE, AGS, DSC and LEW comms. Here's a diagram Qsilver7 posted on another board (and likely this board at some point!).
Doesn't change your H/U install but it's interesting to see how the various buses connect etc. Most aftermarket systems are going to call any of the buses in a BMW "CAN bus" - it seems to have become a generic term for any bus system in a car these days.
The above diagram also shows why it's possible to work on E53 cas with only a low-end KK-line OBD-II adapter - the CAN bus isn't used for diagnostics (except via the bus gateway in the IKE). KK-line adapters are much cheaper that the DCAN units required for later cars.
I also had a good read of a really great document on diagnosing D, I, K, CAN and P bus faults. Man, I'm glad I've got an oscilloscope!
