Jumping gauges
 

I have a 1996 6.5TD with 100k miles. I was driving it today and all the sudden the gauges start to jump around. It would be intermittent. Later that night the the headlights were dim and voltage was low. Once I powered off the lights the voltage came back to normal. The truck runs without a hesitation. Most likely a ground somewhere. Any thoughts on where to start? Any advice would be appreciated.
Video link below:
Hummer Gauges Video by logicbyondreason | Photobucket

Today when i started it the truck the guages did not jump like in the video above. However, when the headlight switch is toggled to either parking lights or lights on the voltage gauge will see a large draw of voltage and the others will move closer to the left. I've noticed the headlights are not bright by any means. It must be a lose wire somewhere/ground. Can anyone point me in the right direction?