Howdy, alternator saga continues, I got it apart and what i hoped to find was some worn brushes in which I do not think I found. Appears slip rings are in good shape and the brushes are making contact. After researching a bit, performed the following:
So what I did:
Tested brushes:
1. One brush goes to ground which makes sense
2. The other brush is connected to (F terminal I think) on the connector in back of alternator. This was the green/white wire that tested at 12v when the tractor was running. This means the regulator was energizing the rotor at 12v which seems proper.
Tested the rotor.
1. Ohms between the two slip rings ~ 5ohms
2. Slip rings not shorting to ground
Tested the stator
1. Made sure had low ohms through windings from each output wire to the join
2. The only odd thing I thought was that I thought each phase of the stator was isolated from each other. Doesn't appear to be the case in this alternator?
Tested the diode plate:
There are "two" plates each containing three diodes in this alternator (two semi circles)
There are three diodes on the plate that handles the B+ post and the other post
There are three diodes on the second plate that handles the other two posts.
Note: the two plates are physically connected to each other through insulated jumper wires.
I set my MM to diode test / continuity, Put the positive lead on on the stator output side, put the negative lead on B+. Nothing
I tested on the other two diodes on the same plate. Nothing
I tested a post on the other plate and got positive result setting pos lead on top of one of those diodes. The other two on that plate checked out as well.
From my amateur stand point, it appears I have three bad diodes. The plate with the bad diodes looks particularly in worse shape (more rust, dirt etc) than the plate with the diodes that work (relatively clean).
I will say, I learned a lot about alternators in this little adventure!
Now, I don't want to track down diodes and replace them and I quick search for the diodes plates turned up empty, so a new alternator looks like in the books for me unless I'm completely off base which is completely possible!
Now to search for an alternator that is a proper substitute. Looks like i'll be rewiring the 4 pin connector to a 3pin from a couple of quick searches on amazon. I see no alternators that have this 4 pin connector.
EDIT: pontification: It seems my alternator would be running at half capacity with 3 diodes bad... I wonder if I can flip what was previously B+ to a differnet post. They are all connected and looks like they all have the same output. I'm only running lights, not sure I would pull 10amps which is what this thing is rated for.
- Mike
check and verify your fuses are good. One of them provides power from the key switch to excite the alternator. 
