2003 GMC Sierra
When key is in "ON" position there are no dash lights engine light only. There is a buzzing noise in dash board I can start the truck fine, and all lights come on. Everything works fine. If I turn truck off, and put key back in ON position everything lights up correctly. If I leave the truck for awhile "hours" then put key in and go to "ON" position again there is a buzzing noise, and no dash lights except engine light. Also while running, the gas gauge will drop to empty. If I shake the truck, the gauge will go back up, then after a few minutes it will drop again. These two things may not have anything to do with each other.