The story so far: I found this truck 60 miles away at a sale. It was getting dark so I ran the engine about 2 minutes and said I'd get a ride back the next day, probably buy it and drive it home. I couldn't find a ride so I called and was told another guy was looking at it. Two days later it was still available, but was now overheating. I drove up, bought it for $350, and had it towed home. I replaced the thermostat and on trying to start it the battery began to die. I found rust and corrosion on a very hot positive terminal of the solenoid relay and the 16ga fusible link to the black/red wire was fried but not open. (When that wire is open everything is dead including the starter.) The solenoid terminal broke off when I put a wrench on it, so I replaced the solenoid, both battery cables and put a 20a ATO fuse (just guessing) in place of the fried 16ga fusible link.
I used starter fluid, the engine ran about one second and died and all power was lost. I found the 20a ATO fuse open. The next day I replaced it with a 25a fuse, left for half an hour and on returning discovered the alternator very warm. I removed the fuse and the alt temp dropped to the outdoor temperature.
I can't find any wiring diagram that matches the truck wiring but I'm sure I got all the solenoid wires in the right place. If so, what could cause the original fusible link to fry, blow the replacement 20a fuse on starting, and the alternator to heat up when everything is off? Thanks in advance for your help.