voltage problem?

["Arts Council" <artscape@clas.net>]

I have what seems to be a generator/voltage problem. My 71 B has suddenly
began idling lower, starting rougher and the engine light stays on or goes
off and on continuely while driving. Also the left headlight is now much
dimmer. I am new to british cars and got into them for the exact reason
that I am writing about. I wanted to learn how to work on them....but I
need to be pointed in the right direction. Any suggestions?
Thanks,
Daniel