You probably did not add the Most cables into the Most loop correctly .
from the factory they are not hooked into the active part of the most loop at the most junction for the cdc.
Explain exactly what you mean by prewiring.
When a cdc is added the most wires that go to the cdc have to be added to the most loop at the most junction .I don't know if a fuse has to be added for power to the power cable that goes to the trunk bundle.
Most
http://www.e90post.com/forums/showthread.php?t=727663
http://www.e90post.com/forums/showthread.php?t=347222
https://www.google.com/search?q=BMW+...VCkMqy2aCK09M:
http://www.1addicts.com/forums/showt...php?p=19256760
A typical dension installation looks like this
http://www.e90post.com/forums/showth...hlight=dension