Check behind the dash to be sure the primary power cable for all of the gauges is tight. Never hurts to unplug the power cable and verify with a flashlight and mirror that the pins within the plug are clean of corrosion. Has any work been done in or around the dash area recently? Verify your ground to the dash is functional as well. Take a multi meter and ground it then run the positive to one of the positive sides of the gauge with the engine running and the dash light switch in the on position. If your light works then you know it is a bad ground.
