What gauge wire is the DC power feed from starter to alternator?

I own a 1985 Buick Century with a 3.8L engine. I am trying to determine the proper wire gauge that feeds DC power to the alternator, which is fed from the lug on the starter. I believe it is 12AWG stranded, but I cannot find any legible description on the wire sleeve. Nor can I find a schematic for this make and model. I need to replace the wire, as it has corroded, and is temporarily connected by a wire nut; the fusable link is still good. Any help is greatly appreciated.