Thanks for that Schizophonic, sorry to say I wouldn't have the necessary knowledge to tap into a wiring loom, probably set the thing on fire !!
I was lead to believe, for economic reasons that Audi fit "common" rear wiring looms to suit varying specifications, models and user requirements, they then tap off and connect the required circuits at the time of vehicle assembly, that would make sense since they have so many models and specifications surely they wouldn't have a separate loom for each variation.......... would they ?
For instance, I believe that the same basic MMI is fitted into almost every new Audi but it is only initialised to the degree of sophistication the buyer is willing to pay at time of order, as I found out when I paid £500 extra for the "built-in" SatNav SD Card to be initialised on my new A3, and then a year or so later the Audi Agency (no names, no pack drill) asked me for another £400 to update the system simply because I complained that the SatNav information was, on 4 previous occasions, completely inaccurate for our local region !!!