dash cluster lights dim randomly!

hey guys, my 89 vettes dash cluster lights dims ramdomly.  Its in all areas.  Sometimes its fully bright and other times its dims down really dark or it turns off fully.  The whole thing does it, but only certain areas at a time.  Could it be the bulbs or a ground?  Any help would be great!  Thanks!!!

Hi there.You know,it's possible one or two bulbs may be bad,but all of them? I'm not sure.You may have a slight ground problem.Damn thing is,electrical gremlins are always a royal pain to find.But I hope you fix your prblem.Your friend,Joe.

thanks joe, I hope I can figure it out too!  You wouldnt happen to know where the ground is for the cluster on an 89