Alternator Light On

AMC Guys (and girls),

I have a bone stock 73 Javelin with a 304.  Last night after driving the car 
then shutting it off and removing the key, the alternator light came on. 
When I start the car the light goes off.  I drove the car from Austin, TX to 
San Antonio andall over town putting at least 250 miles on it and it runs 
fine and seems to be charging the battery.

Any input as to what the problem might be-

Todd Wallis