Gocart869,
The system on your rig seems quite complicated, and it will be hard to draw conclusions until your alternator is proven to be functioning and reinstalled.
A ammeter is a measure of the current being used by the system and should have no bearing on the ability of the alternator to charge.
Ammeters rarely fail, but when they do, they burn up internally and don't allow current to pass. This would be evident. If this meter inside the engine compartment is indeed in series with a dash mounted unit, then it should read the same exact value as the other gauge.
I would bet that this ammeter might be for another circuit that isn't obvious and isn't being drawn off when you turn on the lights etc.
If you get the charging system repaired and electrically protected so it cannot kill itself, then, with some investigation and a meter you can dissect how this thing works.
Emergency vehicles can have all sorts of strange things added to them. This Leece-Neville system was a classic aftermarket upgrade for rigs just like yours...lots of lights, sirens and do-dads to cover any contingency when it came to saving a life for dousing a burning building.
Back on the ammeter...I think if you have continuity between both terminals, you have a functioning meter. They are pretty straightforward. Good luck.
Stuart
