Is it possible that your existing ammeter might still work if the external "conversion" parts(s) are removed.
No matter what the rated output of an alternator is, it only puts out enough to keep the battery charged and supplement accessories if necessary. It is a load seen and measured, as any other load, by the ammeter. We can't be positive if a 1936 ammeter is robust enough, but most folks who use the original ammeters after conversion to 12V have no problem as Kevin says. The experience for that on Stovebolt is mostly with AD trucks. A 1936 ammeter is too "primitive" to be sure of it's use. 12V components draw 1/2 the amps as 6V components, so that would mean the ammeter has extra amperage "capacity". The extra voltage of the components is no factor. The needle deflection my be less.
You can play around with it on the bench to get a feel for which terminals are "IN/OUT" and if it even works, by using 1.5V up to 9V household batteries. You can us a bulb or two as a load to detect movement of needle. A full test to see if it shows charge and if it blows at 12V will take testing under the hood, not in dash. Some folks here may have other test ideas.
The pic below may help figure out which terminals are which. But even the diagrams were very primitive and poorly drawn. Not many actual automotive engineers back then, especially electrical. Some old Model-T and Model-A guys hired.
I think I already made the point about wasting time on a non critical gauge and that in your restomod 12V conversion, an indicator light is WAY better. This does not sit well with purist, but the original gauge will still be there as it is now and no one will know it's not connected. All of the wires that went to the ammeter would be basically connected together with some fused. We can help with that when you get us info on a harness part number. The light tells you if alternator is charging or not. A 1936 ammeter tells you nothing but that.
FYI: wiring for a refurbish/restore/restomod is done very near last.
