HAVE A 94 PONTIAC GRAND PRIX WITH A 3100 PUT ON A NEW ALTERNATOR AND I HEADLIGHTS ARE REALLY DIM STILL DOES IT SOUND LIKE CAR IS RUNNING OFF BATTERY AND NOT ALTERNATOR???
Make sure the battery is good. It can be checked free almost anywhere.
Check for bad body grounds and common grounds, a lot of newer vehicles use a common ground wire to ground many things that are plastic-mounted or rubber-insulated from grounding. (headlights, heater, dashboard wipers, etc etc)