As I recall the starter key to solenoid(grasping at memory) may have been 10 gauge and would draw 30 amps. I found that out after installing a 20 amp fuse, to protect 12 gauge wire in the circuit which connects instruments and alternator line. I know that's wrong(varying gauge wire in the circuit)!
But I think it was common, and not that easy to fuse. You may need to rewire and fuse separate legs on the circuit.
Maybe someone will chime in.