Tip buttons in D are a TCU coding thing and definitely should work on an 02 S8. Assuming the stick is in D (red-circled switch) then the TCU will still respond to the tip signals which it knows are coming from the steering wheel, thus it goes back to D on its own after a bit.
There is a diode in the circuit from the tip-engage switch so that the TCU doesn't see the power to the two lights in the shifter which the engage switch also operates. I wonder if a fault on the lights would cause the TCU to see a stuck ground on the switch...? Still pondering.
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