That's thing. It's not like an ammeter on a generator. The alternator output does not go through ammeter.
I know it says 'alternator' on many Chrysler ammeters. It was unfortunate and confusing choice. It also says 'BATT' on the alternator. Whatchya gonna do.
The ammeter on a car only carries current going to or from the battery.
So the only times current flows through the ammeter is during start and while the battery is recharging.
A small ampount may also flow when stopped, especially at night in the rain, when the alternator can't produce enough power to cover all the needs.