Hi Stuart,
As Richard pointed out previously, a voltmeter is really hard pressed to tell you anything about the charging system operation other than it is (sort of) working.
On the other hand am ammeter is a 'realtime' instrument that tells you if the charging system is operating by showing which direction current is flowing while the vehicle is operating;
From the alternator/generator to the vehicle (+)(Good)
or, From the battery to the vehicle (-)(Bad).
I vaguely remember reading that the real reason the OEMs started using voltmeters was to save the expense of the larger copper wires required for the ammeter as all the current for the vehicle (other than the starting current) passes through them.
I will take am ammeter over a voltmeter anytime, as I couldn't care less what the voltage is, but I really care to know if the vehical is being poewred by charging system or the battery.
Just my $.02, course I'm a dinosaur and kind of set in my ways.
Ted
