As Bjorn says...
First though...
Ya need to completely eliminate the OLD regulator from the circuit.
The alternator SHOULD be charging the battery with just the one LARGE lead connected to the starter post containing the LARGE positive cable from the battery.
If you measure the voltage at the battery (I place my voltmeter upside down on the windshield so I can see it from the driver's seat...) is should read about 12.6. Start the car and rev it a bit and you should see about 13.8 volts or greater. This will mean the alternator is working.
The second lead on the alternator SHOULD be just for the dash light and voltmeter on the dash... This usually goes to the ECM on later models and then is connected to the dash indicators.
If the alternator did NOT show an increase in voltage, then this second lead is probably a necessary teaser to trigger the alternator to work. In either case, we'll get it to work...
Using a '74 Euro and NA schemaic... I find that...
The Brown lead goes to the starter.
The Black/Violet lead goes to the dash guage.
The Red, White, and Black/White leads are now discarded with the Regulator.
I believe all you need to do is locate the existing Black/Violet lead and tie this to the other lead on the alternator.
Having said all this and re-reading what Bjorn just said... we AGREE!
Back to the voltmeter readings... If there is NO increase in voltage, there is a good chance the alternator is defective.
If there is no increase in voltage, I'd take it to a reputable tester and have it checked. If it proves to be defective... then we have our answer.
I would also recommend that you opt for a GM conversion.
http://www.network54.com/Forum/12159/message/1142890167/GM+alternator+conversion
Also note my 2008 update...
Good luck... hopefully we've been of some help and not confused the crap out of ya!