everything is plugged into the ign sw! can't find the other burnt end?
open the manual to the wiring diagram instead, check colors, if the wiring is still original - I doubt there's any wire that originally would have been strung across the radio, but things in that direction would either go to the heater, or out the firewall in the centre, which might be to the starter [hot, violet] or the ignition resistor/coil [green?]
Bill