If you have a 3 wire alternator, you can hook up a light real easy. The small terminal closest to the main terminal on the alternator is the idiot light connection. Run that to a 12v gauge bulb and put a 1N5401 diode (stripe facing the alternator) in between the alternator and the bulb. Now whenever the alternator is not charging, like after turning on the ignition but before you start it, the light will come on, then once its running and charging the light will go out.
If you stick with the Ammeter, use a fusible link at the battery.
