I can get some pics if you like, but here is a more detailed description:
In order to power a DC-DC PSU it needs 12v so you take the yellow wires from the desk PSU and connect to IGN and +12v const. (On the M2 that would be the red and white). THen the ground is black on the molex and black on the m2.
Now to turn on the desk PSU to supply 12v, you need to take wire #14 from the ATX connection on the desk PSU (The ATX connector is the 20 pin big connector that goes to the mobo) and short that out with a ground. #14 is a green wire. Just short it, and on the beast will come. Pretty simple.