Jim - Wire the ammeter as follows: 1 - Connect the alternator BAT terminal to the "+" terminal on the ammeter. (If the ammeter terminals are unmarked, just choose one and connect to it....). 2 - Connect the remaining ammeter terminal to the battery positive. This connection is usually most conveniently made where the battery positive cable bolts to the starter switch. 3 - Supply both the ignition and light switches from the ammeter "+" terminal.
Test by turning on the lights or the ignition with the motor stopped. If the ammeter shows a negative (discharge) reading you are all set. If the ammeter indicates positive (charge), swap the wires at both ammeter terminals - it will now read correctly.