98 Voyager Expresso Charging System Light

I have a 3.3 ltr 1998 Plymouth Voyager Expresso. The battery/charging light is on on the dash. I had the battery and alternator tested and both are good. What shoud I be checking? Any advice would be appreciated.

the pcm controls the fielding of the alternator, you would probalby need to perform a full field test with a scanner and monitored voltage sense