The B+ is the heavy wire. D+ is the small red that ends up in the cluster.

The difference in your readings between the big terminal on the alt and the battery has me concerned whether they are measurement difficulties or real differences. If one is fluctuating and the other isn't, suspect corrosion inside a terminal crimp or a loose nut at the starter solenoid. There should not be any more than a couple tenths of a volt difference, when measured reference the same ground. Better yet, you can measure the drop directly if you have long enough arms. Don't let the meter leads wrap up in the belts.

Worn belts. If the alternator is slipping it won't charge when you need it most, recovering a cranked-out battery. You should hear squealing, but not always. This has fooled me before, but the shiny polished pulleys give it away.

If you had the cluster out, be sure all the plugs are back in solid. If you had the speedo out, check the flex fuse.

I don't know if your brushes are short, but that's the first thing I check. Get a good #2 Phillips, not a worn one.


--
Art Benstein near Baltimore

"Hanging is too good for a man who makes bad puns...
....he should be drawn and quoted."