I'm throwing a link to BobM's very helpful library of diagrams at the bottom of this. You can look over diagrams 2,3, and 4 (Same tractors, but different combinations of V/R vs C/O, mag vs. battery ignition). One of them will help you figure things out.
I'd also suggest you snoop aruond the archives for posts from JohnT. I can't find my direct link to it all of a sudden, but he has posted a very good troubleshooting sequence for pin-pointing problems like yours. He's posted it many times, so it shouldn't be too hard to find.
Sounds very much like your V/R or C/O is either bad or just not wired up right.
As far as your third brush, My Super C operator's manual doesn't address it, perhaps one for a C would.
From the manual for my BN, moving the third brush in the direction of rotation of the armature increases output, and counter to rotation reduces it.
Two cautions in making that adjustment. Book says not to set the third brush any closer than 3.2 bars on the commutator from the main brush. Second is to merely loosen, not remove, the screw on the face of the generator that secures the third brush. The way they put it is to loosen it only enough to take the tension off the lockwasher and to tighten it back down after any adjustment.
My book lists max output for the generator at 13-16 amps cold and 9-11 amps hot.
That said, I think your problem is more ikely gonna be in the relay/regulator, whichever you have, and I'd check that out before messing with the third brush. Try cleaning up the points inside it and cleaning up all the wire connections first, as well as the ground for the VR/CO. I'd even replace it if that fails befoe toying with the third brush. Only caution there is that my completely unscientific assessment from all the past posts on issues like this is that one out of four replacements is bad right out of the box. My own experience has been worse than that! 8^(
And you thought you were long winded . . . '8^)
HTH.
BobMs diagrams
