As has been said it will be a Voltmeter, Ammeters went out with dynamo's if I recall correctly, think sixties.
Never forget however that it is a Morgan and many owners like adding modifications including to electrics.
A simple definition of the Ammeter is that it has to be in series with the battery whereas the Voltmeter is in parallel with the battery and that can be easily traced. Your reading of 14 does sound very much like the charging voltage to me this is a little high but these instruments are fairly agricultural tbh.
Here is a diagram with
Voltmeter courtesy of Lorne.
