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This electrical stuff is pretty simple once you get into it. These are the steps you should follow:

1. Get yourself a voltmeter. This can be anything from a $20 radio shack special to a $5000 Fluke, it doesn't matter.

2. Put the car on a battery charger overnight. Using the voltmeter, verify that you have just over 12v at the battery terminals.

3. Turn the ignition key on and verify that the low voltage light comes on. The way your charging system works, current flows from the battery through the fuse box to the bulb, then back through a blue wire (called the D+/61 wire) to the 14-pin connector in the left rear of the engine compartment, then into the engine wire harness, then to the back of the alternator. Inside the alternator it flows into the field, generating a magnetic field that is required to get the alternator to "excite" and begin producing current. If current's not flowing through this circuit, the alternator will not begin to charge, and the light will remain on.

4. Start the car. At very low revs, the charging light may remain on. When you rev it up past about 1500, however the light should go out. If it does not, the problem is in the regulator or the alternator diodes. If it does go out, you know the alternator is putting out voltage. With the engine running, carefully measure the voltage at the battery terminals. You should see 14v. Any higher or lower could be a bad regulator, bad alternator diodes, or bad connections.

5. The connections are easiest to diagnose. Start with the battery terminals, then check the ground strap from the trans to the body. If you have a good low voltage light, then the charging circuit is probably ok, but if not, check the connections on the back of the oil pressure gauge, and the 14-pin connector. Tons of material in the archives on this, check any from Early S Man for a wealth of info on how the charging system works. Warren also has some good recommendations on how to improve alternator output at low rpms.

Good luck!