Well I got all the parts I need, just waiting for the iphone video adapter.
The multimedia interface I got is an "ERA" one , and to my surprise it has a second input for the reverse camera, and REV12V+ IN (from reverse lights) and 12V+OUT (to RNS-E) so I don't have to build an automatic reverse-camera switcher - score!
I connected it all up including a video in source (a STB outside the car) and the reverse camera, and after going into the on-screen menu of the ERA unit with its "mode" button and telling it that there was a reverse camera connected, everything works - it shows the TV input on the RNS-E when I select TV, and if I feed the ERA REV12V+ "IN" wire a 12v signal then the video out from the ERA switches to the reverse camera and hence of course changes on the RNS-E, awesome. Essentially this ERA unit has Woorlord's switching box built-in.
I have two issues though;
1) the REV12V+ "in" on the RNS-E (pin C-2) has no pin installed of course, is this an Audi part that I can get or should I just use a generic terminal that fits? The plastic connector is there as some other pins are in use, its just missing the crimp terminal for C-2. Is this a really really small male repair wire?
2) I tested by powering the ERA and camera with a stand-alone battery. I cannot for the life of me find a 12v feed which is accessory switched. The usual suspects like cigarette lighter fuse, radio fuse etc, are all on permanently (yes I locked the car, and waited, they are permanent on). I could find some that are ignition "ON" switched (like wipers/washers), but I really want it to be wired properly and be "on" when "accessory" is on. This is to power the ERA multimedia interface and also provision for iPhone charging (USB adapter). I have the factory glove-box 6-stack CD player, and I thought I had naled the pinout on that for 12v and GND, but using those to power the ERA made the CD player behave weirdly.... Anyone have any tips for a 12v accessory-switched circuit? This the last of the B7's (built Nov 2007).
I have not connected anything to RNS-E C-2 yet - dont know yet if the RNS-E will auto-switch to TV when reverse is selected.