From my notes, originally posted by somebody else here.
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For ease of reference, the 8 way Molex 'tuner' connector is wired as follows:

1 - Pink - level (signal strength indicator)
2 - Grey - signal (FM MPX output)
3 - Blue - Power Ant (not connected on wiring harness)
4 - Black - 0v
5 - Brown - TX
6 - Red - RX
7 - Purple - no connection (not used in PCATS tuner nor in factory tuner)
8 - Blue - 12v

If you are unsure of the numbering of the Molex connector, please check Patrick's tuner manual.

The purple wire is probably one of the I2S lines. The other two I2S lines are
actually shared with the AM/FM wires. No clue which wires are what though and
from what I remember it's not even been tested. Hugo said that it was to
support DAB tuners ("DABC" signal on mainboard schematics).