I have a Craftsman 917271011 tractor (1998) with Kohler 15.5HP engine. The ammeter is reading negative while in operation. The tractor does start (after charging the battery). This tells me the ignition, starter, seat switch, clutch switch are all working. The headlights work. I think this means the stator is working. I replaced the battery. Mower starts but the battery will discharge after 2 hours of operation. The tractor will start again after charging the battery. Is there a voltage regulator? What should I check to confirm stator or other electrical systems are working or are not working correctly. Thank you in advance.