front seat airbag - why 4 wires?

[Goran]

Audi wiring is so funny.
I played around today with a continuity meter and the D2 seat wiring loom to find out where the two airbag grounds go.
Well it turns out one goes nowhere
when they reach the black plug, only one continues on, and goes to the brown 10-pin plug under the seat. On the diagram that ground just goes to the chassis ground, so its a ground-to-ground.
So TT 3-pin airbag should be compatable as it also has 3 wires one of which is a ground. Next test will be does the D2 airbag controller like the TT airbag.

Here is a picture of the 2nd D2 airbag ground going nowhere. I have confirmed this on another seat thats still in one piece, same set up.