The gauges have 2 seperate circuits, the sending units for each are what make the gauges display info,(like temp.oil pressure and so on) lights are a seperate circuit, could be lights for gauges are getting ground tru the gauge,instead of a separate ground, try runing a wire to the ground side of the lighting circuit to see if this eliminates the problem. also, also check voltage to the lights, if you are using 2 batteries you may be feeding double voltage to the lights. I would think by the sound of the problem you may have a loose ground in the lighting circuit. hope this is some help.