Reply to Midi Fighter Classic Mods

So I'm a noob with the Midi Fighter. I'm slowly becoming more of an electronics guy, and I am modding my midi fighter. I plan on adding a jack so I can plug an assortment of different unique switches to my device. I want to start out with only one, and I will expand as I see fit. All I need to know is, to trigger a signal in a digital switch, do I close the circuit between the 5V pin and the digital pin? or between the digital pin and the ground?

Cheers,

Twinrova