I have inherited a '57 210 2 door hardtop from my father in law who recently passed and need help diagnosing electrical issue. The battery was dead the other day and since it had been in there for a while I decided to replace it. Went to the auto parts store and got the new battery with a little bit more cold cranking amps. Upon installing the new battery once I hooked up the negative battery terminal it melted a 10 gauge black wire running to the back side of the alternator. I thought that maybe this wire was old and was shorting out some where on the frame or body, so I replaced it and tried the battery again. The same thing happened. Could use some help with this. The engine is a 350 , the alternator says (SAE J1171 Marine) on the back of the casing where the wire in question connects.
IMG_0850.JPGThe wire in my hand is what keeps melting.

Thanks for any input,
Mike