2002 Ford Taurus Intermittent FULL electrical system SHUTDOWN!!!!!!!!!!!!!!!!!

My mom has a 2002 Taurus v6, FWD, SE. It has approximately 110K miles on it. Every so often, (usually while driving at 65-70MPH on the freeway,) the entire.... Yes, I meant ENTIRE, electrical system shuts down... NO instruments. NO power steering. NO power brakes. NO... Nothing.

This has been going on for quite awhile now, and I've tried everything I can think og to fix it. It has NO codes on the reader... I've changed the altenator, checked fuses, changed the battery, checked ignition module, checked the fuses again... HELP!!!!!