Electrical gremlins, again!

Bought a used mini track loader and rock bucket for picking rocks. The "batt" light never came on. Starting and stopping, running in and out of shop, battery got low. I discovered the alternator would excite if I revved engine nearly wide open. Then it would stay charging at any speed.

So, being winter, I decided to look into it. Inside back of alternator was an encrusted mess. Baked on oil/dirt mixture. Then under that was corrosion. I cleaned as best I could, but kind of as expected, found a connection so corroded it busted as I cleaned it.

Did some on line searching, found a new alternator for $100, and ordered it. Put it on, and nothing. Took it off and had it tested, and it was fine. Started checking out machine wiring, and finally found a spot in the fuse panel, right next to the "mini" fuse for the alternator, for a diode. It was not there! Called local auto supply. They were clueless. More on line searching. I knew I'd seen one. Turns out GM used it in the Colorados (we had one for a couple of years). I found one at a local dealer. Now everything works like it should! With the circuit completed, even the idiot light works!

Is it possible the grungy alternator leaked enough internally with grime and vibration it could excite itself?

That's about the only explanation I can come up with...

I have had alternators that did require a high rev to get them going, even with the exciter circuit intact. But never seen one that would excite without it, no matter how high it was revved.