The ammeter is telling you that the charging system isn't working. The best source for troubleshoting and repairing the charging system can be found in the Kohler (not CCC) Service Manual for either the KT17 Series I or Series II, it specifies the use of two ammeters and a volt meter. But basically, what you want to do is disconnect the alternator at the voltage regulator on the flywheel shroud and make sure you have AC voltage of at least 28 volts on the outside leads (measure the voltage between the leads on the AC scale). If the AC is found, reconnect the leads to see if you can find at least 14 volts DC (13.8) at the middle lead (measure from the frame to the lead on the DC scale).
Case 1: If you're not getting the AC volts from the alternator, you have to remove the flywheel to get at the alternator to replace it.
Case 2: If you're not getting DC voltage, the regulator may be bad.
Case 3: If you are getting AC voltage and DC voltage, but the ammeter is still showing discharge, check the wiring for shorts.
A known issue with this kind of charging system is that the magnets that are glued to the inside of the flywheel come loose, then the system only half-works. Be careful removing the flywheel, and maintain orientation of the magnets, glue them back on with sufficient epoxy, and the system will be good (or better) than new.
Been there, done that going on three years of service.