Re-Wiring 1975 Plymouth Duster

That way the needle will point the correct way when the battery is discharging or charging.
When the engine is running, the ammeter should at first show charging of the battery and then center.
If it shows discharging, then something is wrong with the alternator or alternator circuit.
The ammeter is calibrated to indicate 40 amps to 40 amps. Either extreme indicates a big problem. turn off the engine.

To make nice factory like connections, get some open barrel crimpers and selection of Packard type 56 and 58 type terminals.