1983 ford 1 ton van electrical

[gary1955]

I have a class c motorhome built on a 83 ford 1 ton van.
a wire has melted that runs from the left of the engine compartment to the fire wall, thru it up under the dash. i have no power to anything to do with the van. the key switch turns but no power to anything. i think it had a fuse link and looks like someone in the past jumped around it.
It comes from a plug that has 2 wires going to it from under the left side of the engine. I need to know if someone knows if it is the main power to the switch. and how hard it is to replace...I have the thing sold and was running it when it just melted the wire and cut off. I didnt need this with the other work it needs before i let it go to the customer...Can someone shed some light in this for me?