Well depends on how your doing it.? My suggestion below was just for a quick test to prove you have the right connections, which I'm 95% sure is correct.

But if your going to wire it properly then you already have the NO Relay built into the 107 board. That's the purpose of it and it works in conjunction with the Spindle speed.

Setting up in Mach3 is easy enough and you can actually download from PMDX Mach3 XML file which sets it up for you. If you have any trouble here come back and I'll guide you thru setting up mach3.