This is the way the HU receives stalk control commands and sends information to the dash display. (**) Auxiliary input only available on Update List models. The AUX input must be activated in the head unit’s menu. C2 doesn’t exist at all on Tuner List models (***) Models before 2000 have an analog CD Changer audio input instead of SPDIF. In that case, the pinout is as follows: 18=Audio GND, 19=Audio Left and 20=Audio Right.