I am having same issue although not as frequently; my gauge pegs when I first start the car and then settles quickly (minute or 2 usually). Occasionally it will peg while driving but only for a minute. Lights go really bright when this happens so I assume it is not just the gauge itself. I replaced the ground from the wall to the block and thought it helped but the problem reappeared. I have a good ground from the battery to the block but no ground from battery to the frame. If I am understanding this discussion right I also need this? Would going into the radiator mounting screw be a good place? I am obviously new to this, thanks