Thanks for providing this!! Pictures really help.
One caution, I think. Isn't there an airbag in that pillar that the wire might impact if you just stuff it in? Perhaps better to fully remove the pillar cover and tie the wire to the existing wires, in order to avoid messing up the operation of the airbag.
Thanks again for the great guide!
2010 M3 E92 Space Gray, Black Novillo