2000 Mazda MPV

I have a 2000 Mazda MPV. I have replaced both the battery and alternator six months ago when the alternator was showing discharge and the dash light was on signifying a problem with the charging system. The charging warning light has reappeared again on the dash. Tghe light disappeared and I had a 14.2 voltage reading at the battery. The problem is occurring intermittently. I changed the negative post terminal and added an 8 guage ground wire to the body and the tester shows no resistence with that ground. It took me about four hours to replace the alternator and I am not that interested in pulling it again. What advice can you give?
Peter Larson
May 12, 2011.

Have the computer controlled of the alternator's field generation circuit checked and tested-

Jul 2, 2011.