12V Delco alternator problem

[jax55]

If you look at the rear housing you will see a half moon shaped hole. There is a tab in that hole, if you ground that tab and the alternator charges.... bad regulator. Easy to replace.
Bill Williamson is correct, if you lose a diode there will be a definite sound. Still easy to replace.
Could also be you wore one of the brushes out.
All are easy to replace, once you have the parts.