Check to see if the alternator frame is grounded to the engine. On my 1980 there is a wire that runs from the alternator frame to the engine block. Since the alternator has rubber bushings in the mounting arrangement, it is insulated from the block. If the wire breaks, in my case, corroded away, the alternator does not charge the battery, and the alternator light does not come on!. You don't know you have a problem until your lights go dim and you car stops after the battery is discharged.