Quote Originally Posted by jackb View Post
No, the battery light only comes on before I start the car. It does not come on while running despite the low voltage indication on the gauge.

The volts I listed above I took off the jump post in the engine bay (intake manifold for ground).

I just measured the cooling fans current: one is 8.85 and the other is 9.00. (Tested by starting up the car and forcing them on by turning on the a/c).

The alternator tested good when I had it measured the other day.
Attachment 60945

Does this look like an alternator anyway? Or the pulley? (The pulley was replaced by DMCH when I changed the alternator in 2011. The 2.8” I measured was at the outside of the belts groove; what size should the pulley be?).
Or something else entirely?
I'd say the alternator is OK (and the light doesn't come on when the gauge is low because you haven't waited long enough for the actual voltage to get low enough). And since nothing says you are drawing too much power so far, other than low voltage while idling (which goes away when you raise it a relatively few RPM), there is nothing left but the pulley size. Like I said before, we have seen this a lot with the "high amp" D alternators.

V-belt pulleys are measured across the outside of the pulley. (It really don't matter where as long as you measure both the same way since it is the ratio you're after....) You would need a 2 1/2" or smaller pulley to reach 1800 RPM. I would go with 2 3/8" (1954 RPM). Both are common alternator pulley sizes for V-belts.

FWIW- The alternator is probably a GM style/knockoff (that had a serpentine belt pulley). I just checked the pulley on my Blazer and it has a 2 3/8" pulley. There are two very common GM single V-belt pulleys. The (too) large one is usually stamped steel and the one that should work is billet (usually aluminum/steel). The smaller GM double pulleys will work in a pinch. Any alternator shop can hook you up.
If you swap the pulley yourself, make sure the rotor stays forward and does not turn when the nut is loose. This prevents damage to the brush holder inside.

EDIT: GM 2 3/8" at Summit Racing HERE -- Check your belt width and ID before ordering...