My theory is thus:
The CC unit is the low current switching device for the high current relays such as AC cooling fan and AC clutch. My guess is the relays are earth switched and when you hit the mirror switch, which is now dead as it's supplied by the same circuit as the CC unit, it provides an earth path for the relay coils.
But one burning question still remains,
Why did'nt you start with the most simplest of things?
Spoiler
