No warning, just got in, started it and the gauge cluster went crazy, then died and saw that the battery light was on with truck still running.
Voltmeter showes only 12v at batter and 12v at alternator post. Not putting out. So I checked the 20amp fuse 11 and yup, blown. Ha, easy fix right? Nope, replaced the fuse, battery light still on. Still no output from alternator post and fuse has not blown again.
I'm pulling the alternator to bench test it but looking for second opinions. I keep reading about this "mega fuse" but not familiar with it. I know the truck is starting and running just off battery power but would I be able to do that if the mega fuse was blown?
i'll probably just change the regulator if the alternator fails.
2001 4.6

 

it was the alternator. found my receipt on the advanced auto reman with lifetime limited warranty from 5 years ago. out the door with a new one no charge.

 

The first thing that I do in a situation like your's is to charge the battery with an AC battery charger. If it charges satisfactorily then I know I know that it's probably a alternator or vehicle problem. If it doesn't then it's a battery problem.