I'm a little late to the game but if you can get your hands on an OE 3 wire harness, I'd recommend it. I have one I use for my e53 and Business CD (non-Nav) DSP stereo just to connect my XM satellite radio controller.
I have also found from a pick-n-pull yard an OE 3 wire harness from an e46 and even tho it has a different part number FOR this wire, it's the EXACT SAME wire harness for e53 (and maybe E39 or e38). The ONLY DIFFERENCE is the metal pins are installed in different spots on the plastic connector which you can easily take apart and swap positions around for. I just did this myself as I installed some 3000 ohm resistors inline to replace the OE resistor which sometimes gives out making the Wire act "dead" as the stereo then thinks there is NO Aux cable installed therefore doesn't show the AUX option on Radio display. It's a bit common and a topic you can search on this forum (search AUX missing).
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