Do I have a grounding issue? How do I troubleshoot the electrical system?

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I have a huge variety of electrical issues; window problems, yes, but mainly everything on the dash/console doesn't work but the fuel gauge, the oil temp and the radio do work (I may have forgotten something in that list). Think this may be a ground issue, but don't know where to begin to trouble shoot the problem. VERY FRUSTRATED. Also, I should mention that when I drive over a small bump in the road EVERYTHING lights up for a split second and then goes out again. I'm so tired of driving at night not knowing how fast I'm going with no dash lights!!!! Also, the 'low tire' light has remained on since I had new tires put on my 1999 Buick Regal LS. Had that checked couple of times and no tire is low on pressure/air and the mileage given above is incorrect as that doesn't work either!!! Again, very frustrated. Please help me ....where can I get a diagram showing where all the grounds are located on my car???