Try turning on as many accessories as possible with the engine not running- - - -high beam headlights, ignition switch "on", electric wipers if it has them, cigarette lighter, heater blower, etc. The ammeter should swing almost full scale to "discharge". Leave the drain on the battery for 5 minutes or so, then turn everything off, start the engine, and accelerate to fast idle. The ammeter should swing at least halfway to "charge", possibly more, depending on the capacity of the generator and the current regulator setting. If the ammeter doesn't move under these circumstances, you've probably got a bad meter movement.
Jerry