I have a 2002 ZTS that has this annoying headlight flicker that we can't seem to track down. When it happens we notice a drop in the fan speed on the vents and light dimming as well. We just changed the alternator and serpentine belt (and timing belt and water pump) thinking the new alternator would fix the issue. We are also going through batteries quite a bit and usually get a year out of them if we are lucky. What she we check? We cleaned most of our grounds when we had it apart for the belts, alternator and water pump. The car has 196k on it so its hard to say. Thanks!!