2002 chevy suburban with elctrical problem?

[mama ayers]

My suburban began starting hard and having power problems so I had the alternator checked, and as it was bad I had it replaced as well as a new battery installed. That worked for a short time, but now it is acting up again. It has a voltmeter in it and the needle is bouncing all over the place when the truck is running, however if I turn on the lights, radio, heater etc. everything settles down and functions normally. This seems completely backwards to me. All of the fuses and relays have been checked. Anyone have any idea what this is? Thanks

 

[mike p]

Go to you battery, check the ground connection on both ends. May have a loose connection on it.

 

[kmp1171]

this is a strange one! but first thing that comes to mind and i could be way off here is check the serp belt tensioner pully is it bouncing and unsteady if it is good my only other thought would be faulty gauge. check for voltage out of alt is it pretty steady it is gonna fuctuate a little but is in up and down a little in value or is it way up and way down if reading normal then i think gauge if it flucuating excessivly again i wiold looke and tensioner.