Its not hard. The button is what they call a momentary contact switch, like a horn button. I assume it probably only has 2 prongs. 12v+ would go to one prong, and the starter wire would go to the other prong.

On an ignition there is a power wire, than the ACC1, ACC2, On, and Starter wires. Turning the key just connects ACC1, ACC2, etc... to that power wire.