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Sounds like a bad ignition switch, especially since it quits while driving. Replace ignition switch.
Check fuses and swap out relays. There were some problems with water leaking through windshield dropping onto fuse panel and GEM module under dash driver's side left of steering wheel. Check there for corrosion and signs of water contamination of fuse block. See checking fuses: https://www.youtube.com/watch?v=iG-AsEemqD4
See this forum link: http://www.f150forum.com/f12/leaky-windshield-gem-module-problem-twist-98192/