NEED HELP - Truck dead after starter replacement

[jtinpdx]

Hi All,
I'd love some help in trying to figure out what happened to my truck. I've got a 71 C10 longbed with a 350. Last week, it started making awful noise while I was trying to start it. I figured this was the starter motor giving out. It would start but make terrible noise and then run fine. Eventually it stopped starting, so I brought it to my mechanic.

He replaced the starter motor and did some maintenance on the flex plate. I guess the starter motor did some minor damage to the flexplate when it crapped out.

I picked up the truck right after he finished working on it. It started right up and ran great. Radio worked, electricals seemed fine. I drove it straight home and parked it.

When I went to start it the next day, it was completely dead electrically. The clock on the radio wasn't even displaying. Turning the key gave absolutely nothing. The battery is fairly new. I tried jumping it, and it seemed wrong. The jumper cables got super hot and were smoking.

Looking around the engine bay, something about the battery seemed different. Closer look and it seems the battery is now grounded from both positive and negative terminals. Negative runs straight to the engine block. Positive was running to the body. See the picture, but it's hard to see.

So I took the ground off the positive terminal, took the battery out and put it on a trickle charger for a while. Put it back in and nothing. Nothing at all. Same things still happens when I try to jump it. The cables and connections get way too hot.

What could possibly have happened? I'm at a total loss.

Thanks,
Jeff