Wiring Problem

[82 Silverado 4X]

Tonight I ran into a problem on my 82 PU. After unsuccessfully trying to jump start my son's S-10 Blazer with my truck we drove my truck to get some parts and tools. I shut it off for just a minute but when I went to start it, turning the key did nothing. After unsuccessfully trying to catch it in gear we found that the red wire with what appears to be a fusible link that hooks onto the drivers side on terminal block on the firewall was burnt completely off. We twisted the two burnt ends back together and was able to restart the truck.

My question is, could anything we did while jumping my son's Blazer caused this wire to burn off like that? Will repairing the wire by soldering a splice into it be a good enough repair?
Thanks for any advice.