This is the setup I use for testing gauges. It is a 5 volt power supply made with a 7805 regulator and a precision variable potentiometer. I set the resistance I want with an ohmmeter then connect it up and check the reading. Using a variable potentiometer lets you slowly change the resistance and observe the meter movement.
Some things to note are. The meter will move slower than in a car, because you are putting in a constant 5 volts while a car is sending pulse width modified battery voltage. Don't get too concerned about accuracy, because every Instrument voltage regulator puts out a different voltage. Unless the car has an electronic IVR, it's just a piece of metal that gets hot and bends, there's no accuracy there.
