Starter too hot to touch!

[1970stringbean]

We've been having some electrical issues. PO had hacked the ignition circuit beyond recognition. Got that straightened out. Drove the truck (1970 K10) for the 1st time today, since engine rebuild. Got to work shut it off, went back out 30 minutes later and nothing. Crawled under it to make sure a wire hadn't come loose. The starter was so hot it actually burnt my hand! Luckily, I had another starter, swapped it out and made it home tonight. What in the world would have caused this? I am at a loss here, any advice would be greatly appreciated!