I have a 318 and my battery light comes on a lot too. Every time a voltage check at the battery posts with my volt meter has shown over 13v-so the engine is charging the battery.. (Well, actually except for the time I fried the aftermarket voltage regulator)
If you look under the instrument panel you see a rectangular black box. I am assuming that box controls all the instrument panel functions and it is seeing a problem that is not there or is caused by a bad connection someplace other than the charging circuit. It does not affect operation of the electric clutch.
I've lived with that problem for years. If Mother Deere was willing to share the info, I would probably have obtained an electrical schematic for it and looked for the problem.