93 Ford Aerostar alternator light is on you had the alternator check and it comes out good what else should you check?

There are times when the alternator will test out fine as far as amp output and voltage output but if your alternator has a weak diode(s) it may trigger the light to go on. I hate to say you should replace the alternator, but your charging system is pretty much self contained in your alternator so I believe the problem is in fact in your alternator. Good luck.