C60 wiring harness in a K20?

[1968_K20_4x4]

So, today I literally tried to "fire up" my truck. I stopped at the gas station and when I went to start the truck after, it cranked but didn't want to start. I turned the key off, waited for a few seconds and tried again. This time absolutely nothing happened. I tried some troubleshooting which included removing the ignition from the dash for inspection. I couldnt see anything wrong, so I decided to try and start the truck with a screwdriver at the starter motor just to get it home. I put the key to ON and left it there. But once I got out of the truck to go jump start it, I saw smoke coming out from under the dash. I turned the key off and pulled the battery cable to stop the fire. My red ignition wire was burning at the fuse box, as well as behind the ignition switch. See photo attatched ( Sorry that it's not strait but you get the idea)

After calling a tow truck to haul the truck home I went out and inspected and it looks like I fried my wiring harness Luckily that seems to be all the damage that happened. I've had this truck for about 2 years and have never had any issues with the electrical system before

So now I have some questions. First off... what went wrong? Bad ignition switch? When I had the ignition removed from the dash was it no longer properly grounded when I tried to start it?? Or???

Also, my buddy has a 1971 C60 dump truck that I can take parts from. Does anyone know if I could pull the wiring harness out of his C60 and install it in my truck? My truck is a 1968 Chevy K20.

Apparently there is supposed to be a fuse wire coming off the battery that is supposed to prevent this from happening. I don't know if I don't have that or it didn't function properly or what.

I have a little electrical knowledge but certainly not very advanced.

Thanks