Hello, my recently restored 1975 DT125B runs excellent, except the dynamo is not charging the battery. I had someone check the voltage regulator, and they said it does not appear to be working. Before i replace it, what should I check to make sure it's not the dynamo's fault? Thanks.

First & only thought at the moment without knowing more--is generator brushes worn right out until the spring has bottomed on the guide. Does the starter operate as brushes are involved in that too. Good luck.

The brushes are in good condition, and the electric start does work.

Did you do the tests set out in the factory manual (located in the tech downloads)? It has a good walk through for testing and adjusting the regulator.

Pretty reliable system over the years. Regulators never realy play up. Think what i'd do seeing the starer works--is close the cutout by hand to see if it's trying at all, but suspect not. Or hook a fingernail under the charging top plate & pull up slightly which is like adjusting the spring screw down the side. Cut out though you need to push down on the top plate to close contacts down the side. on the face of it i think the problem is elsewhere, just don't know where. Is the charging light on the dash [tacho] working. Is it on & staying on. If not on, i'm wondering if a blown charge bulb would be enough to stop the system charging but very much doubt it. Are wires at the stator connected the right way around. Obviously the starter side is hooked up ok.

I think 2 brushes run the starter and the other two the generator? It's been eons since I messed with one.

Anyway, I've seen the starter work and the generator not work or vice-versa when one or the other had a bad/broken brush or brush wire.

My bike does not have a charging light. I'll definitely dig around in the wires to see whats not going where.

I have not. But, I will! Thanks.