I too had charging trouble awhile back. The car ran with only 6 volts at one point - it never died! I went through the entire system and now its trouble free. Heres what I did:

1. Put a new lug on the big red wire on the battery from charge circuit.
2. Cleaned the 25A fuse on the fender by the battery.
3. Cleaned up all my ground wire connections. The blue wire from the alt. to the frame was loose causing a voltage drop.
4. Removed the alt. and cleaned it with electrical spray.
5. Replaced the voltage regulator/brush assembly with a new Bosch unit - avoided aftermarket.
6. Replaced the alternator belt(s).
7. Soldered new connectors to both red wires going to the alternator.

Most likely steps 3 and 5 fixed the problem but I did the rest since I was in there. All together were talking $50 in parts and 4 hours of time. The only thing I didn't do was change out the 2 mounting bushings on the alternator...