so, obviously something is up with the electrics.  Does the battery-on light mean that there is no charge at all from the alternator, or that there is a less-than-expected charge, or something else entirely?  

The light came on about 30 miles from home, but the van ran just fine all the way home.

What diagnosing needs to be done, and where should I start?  I was thinking of putting the meter on the alternator, what output should I be satisfied with?  Is there any other components back there (diodes, etc) that could also fail, making the battery light  come on?  If so, how should I go about testing those.

This alternator is on a 91 GL.  I'm not the original owner, so I don't know how old the alternator is, but it is at least 4 years old.

Thanks for any insight.

Bob
Marlborough, CT