After a fire.....
One last example.
Engine running, foot on brake pedal.
Ammeter shows discharge. Therefore the system is running on battery power.
Voltmeter is around 12 V. Therefore we know the system is running on battery.
In this case either gage alone provides information that allows us to conclude the same thing. For some reason the alternator is not producing power above battery voltage.
Neither reveals that there is no current flowing to the rotor. That will require diagnoses.
One last example.
Engine running, foot on brake pedal.
Ammeter shows discharge. Therefore the system is running on battery power.
Voltmeter is around 12 V. Therefore we know the system is running on battery.
In this case either gage alone provides information that allows us to conclude the same thing. For some reason the alternator is not producing power above battery voltage.
Neither reveals that there is no current flowing to the rotor. That will require diagnoses.