73 Dart Alternator doesn't show charge anymore.

Lets take a minute and briefly go over Amps and Volts.
Volts are potential energy. The battery is analagous to a water tower. The water in holding tank at the top supplies pressure throughout the pipes when all the valves are shut off. When we meaure 12.8 Volts at the battery with everything shut off, that is the energy level or pressure stored in the battery.
Amperes are a measurement of flow. The amount of electrons moving. If a valve at the bottom of that water tower is opened, then there is flow.

The ammeter shows how much flow is going from the battery to the main junction, or how much current is flowing into the battery to recharge it.

Go back to the diagrams and see the orange arrows. They show flow.