Ammeter to Voltmeter...who does it?
All your alternators output power flows through the ammeter before going to the battery.
Sorry, this is a Misconception! On a Mopar, Jeep and most other cars with an ammeter, all of the alternator's power flows to the main junction and from there is divided up. Some goes to ignition, additional may go to lights, radio, etc.
Only the portion needed for recharging the battery goes through the ammeter.
and the ammeter pretty much stayed at +25 during our entire trip, the first time it's done that.
Something is wrong. First check to see if the motorhome's ammeter is in fact on the charging circuit. Other non-automotive equipment do use ammeters to measure power output (as moparMatt2000 thought). If so, they will be very robust setups.
If it is on the charging circuit, then the possibilites are:
something additional has been wired to it by connecting at or near the battery.
the battery is very low
the ammeter mechanism isn't working right.
While most cars with ammeters have an internal shunt (big metal plate that carries the current), mid to later 70s some cars got externally shunted ammeters. The external shunt is heavy wire, could be in the engine compartment, that the ammeter mechanism was precisely calibrated to match.,
