Rick,
A 6 volt generator won't work. Not enough juice to produce sufficient spark to fire the engine, much less lights and all the other stuff.
If you already have an alternator, there's no sense taking a step backward to a 12v generator.
To check the alternator, take a volt meter and check across the terminals on the battery. Check it with the engine/key off to get a baseline.
Engine off should be at least 12 volts. 12.5-12.8 is a good reading for the battery alone.
Now start the car and rev the engine up. The meter should increase to about 14 volts. If it does then the alternator is good.
You can get a replacement alternator at any of the VW parts houses. I recommend
www.jbugs.com.
Biggest thing is to check the connections on the battery. Make sure there's no corrosion on the terminals or on the strap that grounds to the chassis. This strap is often encrusted with corrosion that can interfere with the proper ground. Take it out and soak it in a baking soda solution overnight, then rinse with clear water, wire brush it to get the gunk out, and reinstall. Or just get a new strap.
