Hi I have an '02 z28 convertible. There is a gauge below the speedo that measures voltage. I've noticed two things. This needle bounces anywhere from 1/8 to 1/4 of an inch in either direction, it is not steady like the other gauges. I've also noticed at night, my headlights seems to flocker a bit just as the needle bounces. thanks

 

It is either your battery or your alternator is about to go out on you. It couldn't hurt to make sure your serpentine belt isn't worn or wobbling on a pulley. Hope this helps

 

i agree with big bird but you also might want to check the wiring also