My dad has a big ford travel van type thing. Last night, it died after he ran the headlights on for a while, so this morning it was taken to autozone so they could test the alternator/battery, both checked out ok. He feels htat the alternator is weakening, because it goes out, and comes back, any suggestions?

 

Voltage regulator Maybe,maybe not.
Keep the belts tight.
Check all the fuses.
Sounds easy to fix.
Good luck.

 

Ya, could be the brushes on the internal voltage regulator. I've had to replace several sets over the years in different vehicles I've owned. A lot of people assume the alternator is bad without checking these first, and it only takes a few minutes. Plus, they're cheap($10-$15 usually).