15V
factory ammeter, is that so?
Most Plympouth/Dodge ammeters have "alternator" on the gage face.
That can be a little misleading.
These ammeters shows the amount of current going to or from the battery.
If the battery needs charging it will show current flowing to the battery until it is charged.
If the alternator can't supply the power, or enough power, the ammeter will show discharge.
That's it.
The meter shows up to 40 amps in either direction.
If you see it getting close to either extreme, there is problem. And if it pegs either way there is a Big problem.