V8-5.4L,Battery good, alternator good, brand new alternator cable, still not charging.

I need help finding out what could be wrong with my charging system. One day my 2003 Expedition didn't start, got a jump start and took it to auto zone to check. Battery voltage was too low to test, so I took battery out and left it out overnight, next morning picked it up, they said battery was good and held charge. Put battery back in and took it for testing, their test said the voltage regulator was bad, so bought a new alternator, installed it, same thing, not charging. Took old alternator back so they could run a bench test, old alternator came back good. So I just recently replaced t