As far as I can remember the colour coding of multi plugs goes like this:
Yellow is Airbags.
Of this I am certain...plugs for drivers and passenger side airbags are yellow...as are plugs under the seat for side airbags. This is the case on my Mk3 Golf, S3 and my Mk4 Golf Recaros....so I'm certain of this.
The A3 therefore should have yellow plugs to signify airbag wiring.
Green is Seat Heating.
Of this I am also certain...for the newer cars!
My Corrado's seat heating plugs are black...but again, my Mk4 golf Recaros have green multi plugs for the seat heating elements...as does my S3.
The A3 therefore should have green plugs to signify seat heating wiring.
Red, I believe is general power.
I seem to remember that my S3 has a red plug for general power and earth to supply power to the seat motors...my Mk4 Recaros are not powered, nor is my Corrado VR6 so I can't confirm...but I believe that to be the case.
Back to the photo:
I would say from that photo that the seat harness is wired for side airbags...whether or not they are actually fitted (they plug into the seat frame) I can't say...but the wiring appears to be there in the seat frame to support the facility.
The seat frame also appears to be loomed for power (brown wire)...but depending upon which convention they are currently using...it could be earth!
But since there are not any other wires in the multi-plug it's not a powered seat...as expected since the seat is indeed not a powered version. This multi plug would have another wire or two if it has electric lumber support, or was fully powered as in the case of an S3.
As for seat heating...you may well find that the seat is fully equipped with the heating pads...but not the control circuits or wiring.
My Mk4 Recaros were fully equipped as are some S3 seats - even those where the car does not have the heating seat option fitted.
To know for sure, remove the seat and look underneath at the multi-plug support panel...if you have a green plug with 5 or 6 wires connected heading up into the seat, you have heating equipped seats...the plug will be obvious!
Providing you have the plug, and hence have heating equipped seats, you could retro fit using the correct loom & switches. Not cheap though! The handy thing is that it's a simple plug and play set up...plug loom into fuse box, into switches and into seats...and turn on.
Or, if you have access to the VAG wiring diagrams / drawings, youi could make a loom from scratch.
