Powering up a xbox 360 -S- power supply

Hi Everyone,

I've got an xbox power supply for the xbox "S", it is only rated at 135 watts. More than enough to supply the RAMPS and steppers. I've cut off the twin barrel connector plug, and found four 18 guage wires inside.

There is 5 volts between the red and white wires, with the red being positive. The two other wires are green and black and show no voltage. The status LED is amber(or "Oranger" as the label says) so it is in stanby mode.

Does anyone know which wires I would need to connect to get the 12 volt side of the power supply to turn on?

Thanks!