I believe one screw on the switch panel should be attached to the dash frame. That's where it's supposed to get its ground. If there is paint buildup on the frame in that location, it might not get a good ground. The frame should be grounded to the car body by the attaching bolts. Again, if there is paint buildup at those locations, you might not get a decent ground. There is nothing wrong with adding extra grounds like you did for the switch panel.