I'm more car guy than Kubota guy but generally alternators produce 14 - 15 volts, for 12 volt systems, and the voltage is regulated by a solid state setup in the alternator.
The one I changed on my 900 looked like a smaller version of a car alternator and was wired exactly like my car ones.
Can't tell you what the relays are for but they probably have nothing to do with the alternator or voltage control.
The light is usually turned on by the internals of the alternator at low/very high voltage. Because you have the proper voltage it's either the wire from the light is being grounded somewhere or you may have an issue with the voltage regulator leaking voltage. The first thing I would do is Google "Alternator light won't shut off" and see what tests some folks recommend. That's easier than me typing two pages of tests. Car alternator diagnosis will apply here as I mentioned above so finding an article specific to Kubota shouldn't be necessary.
Bob
