Electrician's Hardwire Mirror General Mounting Instructions:

All of our hardwired mirrors have the switch contained within the mirror.  No other switch is required.  Also be aware every one of our mirrors tilts vertically and swings horizontally.

Install a 4" octagon box on a CGFI line, flush with the mounting surface at height determined by the user.  The box should be capable of supporting 15 lbs.  (The mirror doesn't weigh that much, but remember it may be on an arm as long as 20".)  Note that the center of the mirror is usually at least half the mirror's diameter above the the mounting-plate center. 

Hardwired mirrors, once connected electrically, are non-refundable.