I hate to be the one to tell you this, but you are in for a little work. I've been there done that. Back in the day, I helped repair several of my and my friends cars with wiring issues.

All the wire in these cars--and all other cars back then--is fairly cheap thermoplastic insulated. What this means is, that if ONE wire gets hot enough to melt the insulation and "toast" as you say, it generally melts--and shorts to--one or two or more wires AROUND it.

If you are gonna fix this thing, you need to pull the ENTIRE under dash harness out, lay it out on a bench, and untape it and inspect it from end to end. Leave small amounts of tape at the points where the harness branches, so you can tape it back up later. If you not the colors that were damaged, and the connectors they go to, and refer to a diagram, you can get a pretty good idea of what happened.