You would not want to use a fuse. I would clean the connection you identified & call it good. unless the system was overcharging then it was just a poor connection that melted that terminal/connection that you found. wouldn't hurt to clean ALL connections/terminals. if you keep the ammeter close to 12 0'clock you will be fine. going from batt to starter relay does take some load off of the bulkhead but renders the ammeter reading inaccurate. some people like that mod some dont. if you (A) keep the bulkhead cleaned (B) keep ammeter needle close to 12 0'clock with the rest of the connections/terminals cleaned you will have zero problems