I fought similar battles a couple years or so back. Fried wiring, ammeter pegged, serious overcharging. Had a mechanic work on it, tried new alternators, new voltage regulators, no good.
Finally converted to an internally regulated alternator & upgraded some wiring, with help from great people on this board. Lemme find that thread (there's a lot of my frustration, but the right answers are there too).
The difference, though, is you are now getting proper voltage at the alternator, while mine was too high before the internally regulated alternator. So maybe not the same problem after all.
EDIT: Here's the thread, hope it helps.
http://67-72chevytrucks.com/vboard/s...d.php?t=772236 Good luck!