Ford's wiring has power to the mirror whenever the key is in RUN or START. The circuit in the inside mirror (or navigation screen) uses the reverse lamp feed (+12V when on) to display the video from the camera.
From what I remember, that mirror is very expensive from the factory, although it's also available in the aftermarket (Gentex 50-GENK242) for around US$340. There's also a 50-GENK352 with a larger screen, and a larger price tag. You could also buy the factory rear view camera, but you'd need to have the factory wiring harnesses if you don't want to run your own wiring.
2016 Ford Escape Titanium 4WD
, Magnetic Metallic, Charcoal Heated Leather, new 9/23/2015
- 2.0L EcoBoost I4, 6-speed auto, 301A, Sync 3/Sirius/HD, Panoramic Roof, Navigation
- Husky WeatherBeater 99741/23741 mats, Ford factory splash guards2008 Ford Fusion SE FWD
, Black, Charcoal/Red leather, new 2/23/2008, still strong and trouble-free
- 2.3L I4, 5-speed auto, Sync, Sport Appearance/Moon 'N Tune/Ambient Lighting packages, Husky WB 98301 mats2013 Ford Escape Titanium 4WD, Ruby Red Metallic, Charcoal Leather, new 11/2/2012, sold 9/23/20152010 Ford Escape Limited FWD, Black, Camel Leather, new 4/22/2010, sold 11/2/20122007 Ford Edge SEL Plus AWD, Blazing Copper Metallic, Charcoal Leather, new 6/18/2007, sold 4/22/20102005 Ford Escape Limited 4WD, Redfire Metallic, Pebble Leather, new 6/4/2004, sold 6/18/2007