Do you have a generator or an alternator? A 53 was manufactured with a 6 volt electrical system with a generator. Someone has obviously done some rewiring, and they might have bypassed the ammeter in the process. Some less than well-informed spark chasers believe that there's some sort of hazard involved in running the battery charge/discharge current through a dash-mounted ammeter.
A AAA battery, even at a dead short, won't have enough current capacity to deflect an ammeter more than a fraction of its full scale. You could try a D cell instead, but that's a really bad way to check things out.
Jerry
