I have a 1999 Ford F-150 4x4 4.2 V6. The battery light comes on when the engine revs over 3300 RPM. The battery and alternator were check at Advanced Auto parts and everything was okay. I have 52000 miles on it and they suggested to try a new belt. I did and that did not help.

 

sounds like maybe the voltage regulator. just a guess...good luck

 

Definitelt sounds like a voltage regulator, also, check the tension on your alternator belt, it may be too tight. Hold a ruler don the belt long ways, and take another ruler and press the belt down directly on the side of the first ruler. It should go down about 1/4 of an inch, if it is too tight, it could be causing the problem too.