Not usually done that way, seems too much work, easier to just hook into existing illumination lights from another gauge in the car, or ciggy lighter illumination etc, doesn't matter where from, just be aware that if on a circuit that can be dimmed, it will also dim the gauges you connect to it, earth similarly can be taken from a convenient earth wire nearby, that's how I'd do it, it will also be protected by the fuse serving the circuit you connect into, the small amount of current used for illumination will not be an issue, unless you have gone mental on the amount of gauges!!
tabetha