Yes you can use a fuse. Amperage would depend on alt output and your current draw. IE do you have elec fans, fuel pump, etc. The higher the draw the higher fuse rating to keep it from blowing. Also when you think about it, a fuse or link really does no good as you have 12v power coming from both directions. So a short will have power coming from the bat as well as the alt. This issue has been debated many times on this and other forums...