I tend to do research after asking the question, so I found the section, and there are lots of good diagnosis and maintenance tips in that section, so thanks! I got two brushes from a starter and alternator place for free, that are the same dimensions as the OEM one, except a bit wider. I just need to file it, crimp an end on and put it in. Any installation tips?

I’ve wondered about finding other sources for brushes myself. I would think that providing they were dimensionally the same and the lead was proper gauge with insulation, it would work. Maybe post pics and part no. On that. What’s nice on installation, is that you can keep the brushes pulled back with the spring along side until you have the generator back over the armature, then release the brushes. Just make sure your wire can move freely.

Ps, the search function will bring up a lot of good information as long as you find the right search wording. That’s key. Sometimes it takes 4-5 ways of description before you hit it. The best threads have a successful ending posted. Some don’t, so how do you know? Was it successful or did the guy give up?

Funnily enough, the brushes I acquired have a wire in a very similar gauge as the Yamaha brushes. I will have to cut them to length, and crimp an end on. On my Dynamo, I could actually remove them from the outside, and so I think, replace them from the exterior as well. My bike is a 1974 DT 125B.

Not to nitpick or anything, but the DT-125B is a 1975; the 1974 is a DT-125A. Your manufacture date may be in 1974, but the model, if it's a 1975 model, is a DT-125B. Might make a difference as the 1974 was a one off year in many ways. The 1975 has much more to do with the bikes that come after, I think, than the bikes which came before, though less so than the bigger bikes.

How can I tell, what are the differences?

My experience consists of 2 complete Dt125a s and one very incomplete dt125b and much study here. I would guess the dt125c would be more of a one off than the previous 2yrs. The 74-75 seem to me to have much in common with 69|73 Ats overall. I only submit this as a discussion to learn, not to argue.

As I am remembering, the 125 has more continuity than the larger displacement bikes, so you could be right.
The 1975 125B looks a lot like this:

The 1974 125A looks more like this:

Mine is definitely a 1975 DT125 B

Update on my Dynamo: I fabricated a brush, and installed it successfully. However, no spinning yet. I am getting power to where it needs to be, and I have continuity between terminal A and F as I should . However, I do get it between the yoke and the positive brush, where I shouldn't. Any ideas, or advice? Thanks.