I have replaced the alternator 3 times in 3 years. This time instead of the battery light staying on it only comes on when I accelerate & the RPMs go above 2500. Someone at Advance Auto told me it could be the tensinor this time which is cheaper to fix. Anybody experienced this. Both battery & alternator checked out OK when I had Autozone look at them with their guages.

It could be a bad tensioner

or it could be the belt or
Check with help from Autozone

or it could be the alternator went bad because you do not have the extra splash shield installed
Splash shield issue


or it could be the reference voltage wiring issue.
Duratec Maintenance FAQ
Alternator wiring fix