This alternator deal is easy to fix.

Alternator bearings on the D21 were about to give up the ghost so I dug into it this summer. The OEM was a regular Delco with an external mechanical type regulator mounted in the dash console. Somehow, while trying to press out the front bearing on the old one, I broke the front housing so I trudged down to the NAPA store and bought the cheapest rebuilt 10SI Delco that they had in stock ($38).

Once you have the 10SI mounted, hook the battery charge cable up to the output post on the alternator and run a jumper, as pictured, from that post to the proper terminal. Crank up the engine, rev it a bit to excite the alternator, and you're in business! 10SI conversion instructions on the Internet all seem to say that you need a "special" regulator, but I think all that is necessary is to have one with enough internal "leakage" to start charging. Some available on eBay are advertised as being able to energize at lower speeds. Those would possibly discharge a battery quicker if left for long periods. The high speed energize type may discharge less, but either case would probably not make much difference, even with the tractor sitting over winter. In any event, the bargain type NAPA rebuild seemed to have a self energizer type that suited my application.

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