Dash flicker, then nothing....

[YXLSLT]

Had the flickering lights and all when I hit bumps in my 2001 Yukon XLT. The other day they went off, speedo, tach, mph everything on dash. I've read about checking the harness and the wheel to the dimmer switch. When I check those what am I looking for? Am I OHMing it out or anything? Checking for 10v coming in? Im going to check my grounds, what all grounds do I check?

Any help is appreciated.

thanks