Any electrical guys out there?

[phishfud]

Just had a problem with my 84 K10 yesterday. I had pulled the battery out to use in another car, and upon putting it back in the truck, and starting it up, I saw smoke by the junction box on the firewall. There is a wire coming off the j-block, that ggoes into a fusible link, and splits into two red wires. The two red wires are fine (one to alt, the other to light swtch, according to the FSM), but from the link to the j-block the wire is melted and broke. The alternator was smokin hot, after only less than 30 seconds or so of running, and the volt meter in the dash showed it charging at 18 volts. I did a serpentine conversion a while back, and added a CS-130 alt. I have been running this setup since proabably last August with no issues. Is it possible the alt went bad, causing the overcharging issue, and burning out the wire, or should I be looking at something else. Gonna take the alt to get tested, but thought someone may have a clue as to what happened. Thanks for any help.
Terry