Electrical problem

[classictrade2]

Last night when I was going over my 1976 Seacraft 23' inboard I noticed a problem. I looked at my alternator and found the jumper wire going from the main lead post to the top of the alternator was completely corroded and broken off. I also checked the main lead coming from the battery positive side directly to the main terminal on the alternator that the jumper wire also attaches was corroded almost completely off at the battery. All other wires attached to the positive side of the battery were also corroded almost beyond repair. I am not sure if the jumper wire on the alternator was in good shape at the beginning of the season, but I am sure all of the other wires were in excellent shape at the beginning of the season. My volt meter has been showing good charge throughout the season. What could possibly be causing this severe corrosion problem? I did see that the main wire coming from the positive side of the battery directly to the alternator was attached to the house battery and not the cranking battery which seems odd but the batteries are set up in series with the negative terminals attached by the negative terminals. Where do I start looking to solve this problem?
Thanks for your help.

Arthur