I've been reading up on I-Bus at "Hack the I-Bus" and openbmw.org. It seems that the steering wheel multi-function buttons communicate to the radio head unit via the I-Bus protocol. So, it got me wondering if such a retrofit could be done to the Z3?

basically, on the Z3s w/ the M steering wheel, the tabs can be replaced with tabs that have the multi-function buttons (volume +/-, track +/-) from an E36 or E39 that had the M steering wheel w/ multi-function buttons. The buttons probably run to a control unit that sends out I-Bus message packets to the head unit for each of the button's functions.

Question is then, what are the BMW P/N for the multi-function steering wheel tabs and buttons and the control unit that translates those button presses to I-Bus messages? Can someone help me find these part numbers?

Everything connected to I-bus is connected in parallel, so there's not issue in adding another component to the bus as long as the total number of devices is under 254 (the address scheme is 8bit wide but top and bottom addresses are reserved for broadcast signals).

Also, will the head unit on the Z3 actually recognize the I-Bus messages for volume control or track advance/rewind? This can be easily tested by hooking up to the I-bus w/ a laptop (say, via the phone connector) and manually sending out the volume control message to see if it responds. The data structure for these I-Bus messages are documented so that's not a problem.

What are other people's thoughts? Has this been done? I did a search but didn't turn up much...