Fuses, Circuit Breakers or nothing at all?

I once had a car audio fuse between the alt and starter relay. When I painted my engine bay it look out of sort so I did away with it. As of the moment I have 4ga wire from the alt to the starter relay so I think I need to do something to have protection. I have done the amp gauge bypass. Basically this is what I have.

http://madelectrical.com/electricaltech/amp-gauges2.shtml

As you see in the diagram it calls for a 14 ga fusible link between the alt and starter relay. Now in my situation I have 4ga wire............ how do I go from a 4ga wire to a 14ga fusible link? Wouldn't this defeat the purpose of the 4ga wire? I was thinking of a circuit breaker but wasn't sure what amp I need. I run a 75 amp alternator and the battery is located in the trunk.