2001 cougar battery light

im having a problem in my 01 cougar with the 2.0 liter 5 speed. the battery light comes on between 2000 and 3000rpm's. it had a warn belt which i had replaced along with a pulley which suddenly went wrong the other day at the end of my 3 hour trip. the car also seems to wanna cut out and stall when regularly driving since the light came on. i had the battery and alternator checked and was told they are both fine. if anyone has had this problem or might have any knowledge about what it could be please let me know. thanx.

Bad battery cables?
Bad belt tensioner?

it s the voltage regular. you need a new alternator