boost gauge wiring

hi all

i have bought a electronic boost gauge,the one with the stepper motor but the wiring diagram is confusing me a bit.

the gauge has 4 wires a red a yellow a green/white and a black. ok the black is earth the green/white wire goes to the sensor but it says that the red and yellow wires both go to the  ignition switch, i presume this could be any point that is only live when the ignition is on? also the sensor wires say red to ignition green/white to gauge but it says the black is to be connected to the earth on the coil can this be any earth point? does this sound correct.?or is either one of the red or yellow wires meant to be live all the time and one only live with the ignition on like the red and yellow wires on a cd player?.i also presume that the gauge will be lit up all the time as there is no wire to the dash light circuit. any help appreciated.