When I turn on my headlights while im driving the lights dont stay at a constant brightness they fade in and out real quick, the battery gauge on my dash also bounces around and the inside dash lights also fade in and out. But when im not moving and in neutral the lights dont fade and the gauage stays constant. I bought the car about two weeks ago and im thinking the person ebfore me could have put an alternator pulley on, would this be the case?

 

The alternator might just be going out, easy fix.