I've done it! Almost...
Once again, folks, I'm reviving this thread... but this time its a little more technical.
I have just retro-fitted rear electric windows into my car. I will eventually post the details of how I did it along with lots of pictures, but I'm not quite there yet.
For the last few months, there have been two A2s in the family; my car without rear electric windows, and my sister's with rear electric windows. It's nearly time to sell my sister's A2, so I decided to embark upon a mission to swap the window mechanisms. They both have the same interior colour, so there was no issue with just swapping the door cards over. Both also have the same CCU version; version Q.
The mission is (almost) complete, in that I've done all the wiring and the rear electric windows now work perfectly in my car. I can open and close them with the remote key, etc. Hurrah!
Those who have access to ElsaWin (Current Flow Diagrams) will see that the rear doors locks are connected directly to the CCU on cars which do not have rear electric windows (and therefore no rear door control modules). On cars with rear electric windows, the rear door locks are connected to the rear door control modules and are therefore controlled over CAN Bus.
My car also currently locks and unlocks the rear doors as it should, but when I open the rear doors, the interior lights don't come on. Also, if I lock the car with the rear doors wide open, the car flashes its lights to say "yep, I'm a happy A2", when it obviously shouldn't! If I install my sister's CCU into my car, this issue is resolved. So, this suggests that my own CCU still expects to have direct contact with the rear door locks (and microswitches).
The obvious answer to the problem is simply to swap the CCUs and have the keys recoded. However, I'm puzzled. How exactly are the two CCUs different? I had always been under the impression that CCUs of a given version were all identical and that car-specific options were done by coding alone. However, there doesn't appear to be a coding option which corresponds in any way to whether a vehicle has rear electric windows or not, and therefore whether the CCU should handle the rear door locks itself or whether to communicate with them over CAN Bus via the door control modules.
I'm all ears to anyone who has the answer to this. Are the CCUs in cars with rear electric windows physically different to those without? Is there a deeper level of coding which I don't know about?
Many thanks,
Tom