The Touareg turned out to be the radio in the right rear had blown the MMI fuse, our local VW dealer wanted to fit a new MMI unit in the glovebox which was about £6K... I did it with a used radio and codded it in with ODIS for a tiny fraction of that.

Last week we had a 2009 A4 in with almost totally dead electrics, just a faint image on the MMI and a flashing e brake brake light in the dash. I traced it to a large red cable power junction below the right rear light unit (cheap Chinese LED things, all rusty and wet) where water had corroded the battery to car split coupling, tellingly in 2010 the design changed.