You'll still need a resistor for the other gauges, but you'll have eliminated a potential source for a fire to start. Bypassing the ammeter and installing a cable with a fusible link from the alternator to the starter relay will take a large portion of the charging current away from passing through the bulkhead connector, which can be another source of overheating. This is often done with a stealthy voltmeter installed in the place of the ammeter.