A decade ago, I owned a M35 gasser. I installed a new M35A2 wiring harness, for the turn signals, and to ultilize more modern components like the alternator. It worked great until one night in the dark I accidently shorted something out BIG TIME, with a misdirected STEEL tool...DOH!
Looked like a arc welder going off, not a good thing!
What ever I did fried the alternator, it now pegged way over into the GREEN when I fired up the truck, and the batteries (Optimas) began to "boil" almost immediately.
So my initial guess, based on my experience, is possibly your alternator went South. I don't know ANYTHING about electrical stuff, so hopefully someone else can chime in to tell you how to check it.
In my case, I bought a used but "checked out" alternator, and installed it, and never had another problem, kept the same batteries for two more years until I sold her.
Another time while driving my M52A2 "Mongo" sparks started falling from under the dash. Someone in the military had tapped into a hot wire, and later when they surplused the truck must have removed what ever the wire went to, and left the wire bare.......THANKS!
That short fried the alternator, but before I realized that it was over charging, I burned up every light bulb in that truck, and boiled the batteries pretty well (not Optimas). Removing the excess wiring, replacing the altrnator and ALL lights, and I was back in business.
So when I hear stories like yours I automatically suspect the alternator. That may not be your problem, but I'd look there first.
Hope this helps - Tom
