Did you have the alternator tested. Most supply houses will check alt and reg for you before you purchase. Assuming the alternator is OK, have reg checked, as well as check the wire harness from the alt.
[color:blue]68 GT500</font color=blue>
[color:green]68 1/2 CJ Coupe</font color=green>
First, check the voltage at the battery posts while the engine is running. If there is 13 volts or more, the alternator is working and the problem is with the wiring (stator to regulator) or regulator.
If not, possibilities are a bad regulator, alternator, or wiring. You can either have the alternator and regulator bench checked or you can trouble shoot with a multimeter.
To check the alternator:
Disconnect the 4-prong connector at the regulator. Check to ensure there is 12 volts at the "A" terminal on the connector. Put a small jumper between the "A" location and the "F" location at the connector. Start up and put your voltage meter on the battery terminals. Should have around 15 volts or more. Only do this momentarily since extended running will boil out battery. What this does is send full voltage to the rotating field and generates maximum voltage. If voltage at the battery remains at 12 volts or less, the alternator is not working or there is a break in the 4-prong connector-to-alternator field post wire. If the alternator is working, move on to the regulator.
To test the regulator:
With the ignition key on (engine off) there should be voltage at the alternator "FLD" post. Since your warning light is on, this circuit is probably OK. With the engine off, check the continuity of the wire that goes from the alternator "STA" terminal to the "S" terminal on the 4-prong connector. If this checks OK and all connections are clean, the problem is most likely the regulator. When the alternator comes up to speed, current from the "STA" terminal pulls open a relay in the regulator which puts out the dash light. If the relay is faulty the light might stay on even though the alternator may be working.
If you are sure the alternator is OK, next likely suspect is the regulator. Might just change it out and install a solid circuit unit.