You could pull out your Alternator and have it tested at a low rpm to see if it will charge. If it charges OK during that test there is a good chance you are haveing poor connections in you wires or grounds.
In the thumbnail below at your Alternator Connector you should be getting Battery Voltage in the 2 big slots that go to the fat Red Wires all of the time.
The Skinny Blue Wire and the small slot are connected to your No Charging Warning light and you will only get voltage there when the Key is on.
You have to go way to the end of the article to the last paragraph where it tells you the importance of the Blue wire, the Bulb and that circuit when it comes to charging.
The Alternator Electrical Connector/Plug will come apart as it snaps together. I would have a good look at it to see if it corroded or gummed up inside or just plan needs cleaning.
http://www.pelicanparts.com/techarticles/914_alternator_troubleshoot/914_alternator_troubleshoot.htm
In the other 2 pics I made up a electrical Test Cord to plug into my Alternator that acts like the circuit you would have if your Key was on. You need a least a 3 watt bulb in the Blue Wire Circuit to mimic your No Charging Light. The Red Arrow points to the Bulb.
The above would tell you if you have any wireing problems getting the positive voltage to your Alternator.
Next would be to clean the grounds connections.