Like mentioned above...you need the round pin to flat pin adapter. Get the BMW 11 digit part number...then shop using that number to zero in on the correct part if shopping online (google it by typing "BMW xx xx X xxx xxx"....where X= the BMW part nbrs).
And the MID is another question separate from the in dash CD player. The MID is NOT the radio...the radio is incorporated into the in dash CD or cassette unit.
The MID comes in 2 configurations plus it has options. You need to keep the same button/option set-up. There's a high MID (has the BC icon next to the clock face button on the lower right side)...the low MID doesn't have this icon or function. Then there's the DSP option...which has the "DSP" acronym on the upper right button next to the AUDIO icon. Again, if you have DSP...you have to install another MID that also has the DSP option button.
See item #1 in diagram and link to part database below:
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