Thanks Adrian.
Lucy Cutler has been very helpful & says that 2cvs in the early ’50s had ammeters and that voltmeters were used in later A series vehicles.
The ammeters had no calibration other than a fat white arc for ‘Charger’ and a thin white arc the other way for ‘Décharge’.
They were made by Jeager and ED to an almost identical design but with the former having a larger dial and they had different shapes to accommodate the screw holes to fit in the dash.
While a voltmeter has the benefit of illumination to accompany the speedo I am inclined to fit a 2nd hand motorbike ammeter to be more original & too enjoy watching the current flow!
best wishes, Jamie .