instrument panel cluster problem

hi, I have a 1998 caddy sts with 150k on it. The instrument panel guages will sometime totally not work, such as the speedometer, etc, then sometimes it works fine, i dont know where to begin diagnosing this, could something just be loose, i read to check the body, starter ground, where should i find it? any help would be great


thanks

I have the same problem on my 2000...panel lights go out  usually a/c konks out and radio quits....it comes and goes sometimes several hundred miles between malfunctions...usually i stop turn off and restart it and seems ok
Any Ideas?
thanks...