[dmjlambert]

50 watt resistor is not near enough for realistic loads. The best resistor to add would be a length of more 12 gauge wire. Add another 6 feet and fold it inside the wire holder that runs across the radiator top, and the needle will move about twice as far. I suggest don't worry too much about the 4 amp fuses. Their only function is to blow if the 12 gauge wire actually gets chopped in half or completely disconnected, and then you would be trying to run stuff in the cab or charge the battery through the ammeter, which would be the only remaining circuit to go through. Normally the ammeter circuit carries no significant current, it just gives you a voltage difference reading.