2001 - Alternator shot? - Follow up!

My headlights were severely dim when I parked tonight, the dash lights come on above 2,000 rpm and then off as soon as it downshifts. The alternator is from a 2006 legacy, it was an upgrade at the time to 110amps from 75amps, and has been running fine now for the better part of three years. What I can't figure out is how the positive terminal wire got so corroded, and burned a hole in the rubber terminal boot.