Not sure what year your tractor is, but this may help.
http://www.tractorbynet.com/forums/...electrical-schematic-2005-2005jinmawiring.jpg
If you are seeing battery voltage on the output wire on the alternator, either the alternator field/stator is at fault, or more likley the regulator is not feeding current to the field to generate alternator output. Why the reg is not doing that is the real mystery. Garbage in = garbage out, so along that line you need to make sure the regulator has good connections and all it's inputs. There is a REG fuse on the fuse panel that powers the regulator. If the regulator is on the newer style power panel(uses blade style automotive fuses), it is the little module with heatsync fins plugged in right beside the fuse panel. Mine actually vibrated loose once and I almost lost it if I hadn't noticed it at a weird angle when I stopped to clean the radiator filter while brushhogging. It now has a large ziptie securing it in place...