Fuse links for me are a problem, some of them are not specifically rated. IF the alternator is NOT a "one wire" a no8 would be plenty large. If it is, I'd run a 6
You need a fuse link that will handle alternator output without jeapordizing the wire you are using. What you want to protect against is "if" the alternator (diodes and stator) generate a serious short to ground
