Hello,
I have a lovely little red Zed, with an interesting story: it was imported from Japan, and is the BMW Japan 15th Anniversary edition. It has a 7-speaker stereo, that was not available in North America or Europe, to my knowledge.
It already had an aftermarket stereo installed when I bought it, but only the 2 footwell speakers worked. On removing the aftermarket stereo, I saw that the wiring harness from the stereo did not match the pin locations on the car-side wiring harness. The radio-side harness is the correct one for NA/EU 96 Z3s, so it is an understandable error.
I suspect that the wiring harness used is that of another BMW model, since I doubt a specific harness was made for the Japanese market (although it could have been). I am posting a picture of the car-side harness connector, so maybe someone can recognize it from their experience changing a radio on their not-Z3 BMW.