The wires going into your gauge cluster should have an L/R colored wire. Which for Oreion motors is a Blue with a Red tracer wire. If you can cut it and put a potentiometer in that will vary the power to the light bulbs. That way you could achieve what you would like to do to vary the brightness of them. You will only be able to vary incandescent bulbs. If the backlighting of the gauge cluster is done with LED's then it will not work. LED's would require another circuit and lower powered LED's to make your lights dim.