I've been looking at the electrics of the 94 740i and it strikes me as if pin no 4 on the radio is actually the mute function which is directly interfaced to the wires of the cellular phone.

The blu/yel wires from the cell phone interface directly on the 4th pin of the radio which is the mute function. So by the looks of it when a call is received the ringing alone is enough to mute the radio..

The critical question is which is the pin on the cell phone that gives such signal. Also while I will try to talk to my mates in the labs does anybody have any idea about the power of this signal. My guess is that the signal from any aftermarked cell phone on the hands free kit should be enough to mute temporarily the radio...

What I would like now is to interface the sound of the cell phone onto a line input of the radio...

anybody knows if there is such input on the standard bimmer radios for 94?

Cheers

TheoP