Think I can help you, as I've just been tinkering round this area.
your green wire should have a black stripe on it and your white should have a light grey (slate) stripe.
the black is ground (chassis earth, battery negative).
green goes to your gauge, black goes to anywhere on the frame and the white goes to the loew fuel warning light.
Not sure which goes where but if you have a multimeter that can measure resistance, measure between any of the 3 connectors. If you get a reading between 50 to 300 (i think)ohms or so, green goes on one and black on the other, and white, by elimination goes on the one left over.
failing that, use trail and error, if you know your tank is half full or whatever, try connecting it up till it reads half full on the dash.