Excursion Shuts off when put in reverse and when I turn my head lights

I have a 2000 Ford excursion and when my AC Runs in the hottest time of the day it will not have power and while driving it will shut off .

There might be a wiring problem. Either shorting to another wire (like a reference voltage wire) or to ground. Who knows!? I have a 2002 Excursion that would often die when you put it in reverse (got worse and worse until it was almost a constant problem) but when I wired up a bypass power wire from the battery to the MAP sensor power wire (feeds back to provide power to various sensors in all likelihood). After doing that, the problem went away (runs okay in reverse) but I have to manually disconnect the wire when I am not using the truck to save it from battery drain.