front seat airbag - why 4 wires?

[Goran]

sorry for delayed reply, thanks!
I am now looking at this again. Strange how Audi wiring diagrams dont match the actual wire colours.
It now looks like the D2 seat airbag is single stage, but has two earthing wires?
The Audi TT airbag is also single stage and has one earthing wire. So looks like this will work.

Whats confusing me at the moment is that the Elsa wiring diagrams for TT Mk1 do not match the actual TT airbag wire colours. I have so far tried looking up all TT's from 1999 to 2004 in Elsa, they all say the seat airbags have the driver's = green+, white-
passanger's = white+, blue-

But both of my TT seats have airbag wires black, blue (and the brown earh is the same). Also all the TT Mk 1 airbags I can find on ebay all have black, blue and brown. So how the heck do I know which is + and which is -?

unless, of course, the wire colour is from the plug on the controller side, not the plug on the airbag side?