Alternators without internal regulators almost always have some mechanism so that you can bypass the regulator and see if the alternator is OK. Some have a hole in the
back that you can stick a screwdriver into and short a tab to ground. If the voltage comes up, then the regulator is probably bad.
My experience has been that it's best to just pull the alternator off and disassemble it. Reason is that an alternator with blown diodes can cause the regulator to fail, so you'll
just keep replacing regulators when it's really the alternator that's bad.
Once you take the alternator apart, there are a few simple checks that you can make with your ohmmeter that will nail the problem 99 percent of the time.
First, inspect the brushes to make certain that they aren't simply worn out and that the leads aren't broken. Note that a burned up brush lead can be symptomatic of other
problems, so don't stop there.
Take your ohmeter and check continuity through the rotor (slip ring to slip ring). Then check between a slip ring and the rotor shaft to make certain it isn't shorted.
After the brushes, the diodes are the most likely culprit. Your alternator has six diodes; each one is an electrical check valve that only allows current to flow in one direction.
The diodes need to have one lead free when you test them; on some alternators it's just a matter of taking some nuts loose, while others require you to desolder the diodes
from the stator. Test each diode in both directions, it should show continuity one way and open the other. If you have a digital meter, be sure and use the scale marked with a
diode symbol, the other scales may give false open indications.
Some Delco alternators also have a "triple diode", which is just a small device with four leads. (I think it was used to run the alternator light.) Test it with your ohmmeter; treat it like three diodes with one lead tied together.
The stator seldom fails, but each of the three stator legs should show continuity to each other, and the stator shouldn't be shorted to ground. You probably can't test it without
disconnecting the diode pack.
That's pretty much it. You should be able to get parts at any place that rebuilds alternators.