If your charging system uses a simple 2 wire Cutout Relay and the combination Low/High charge and light switch YES it should charge at a low rate on LOW and a higher rate on HIGH. For that to happen the light switch needs a good ground, be working, and the wire from the gennys FLD post wired to the switch correctly.
If you temporarily jump the gennys FLD post dead to ground that should make her full/high charge and if it does but NOT when using the switch, the switch is bad or miswired or not grounded or the wires bad from genny to the switch.
As posted below an ammeter wont read the correct charge into the battery or out of it unless the battery is on the Supply side while the gennys output (its ARM post via the cutout relay) is on the other Load side.
Regardless if the ammeter is wired right or works if she is indeed charging the battery voltage should rise from 6.3 volts setting (or low idle) to 6.5 to the 7 range at wide open..... John T