Danny: Welcome to the Boards.
Unless I missed it somewhere, I did not read whether you had a MICS or a CICS.
Although if it has a PRI it must be MICS.
MICS - pair 19 Yellow/Brown off the 2nd Station Calbe
CICS - pair 25 Violet/Slate off the station cable (Just FYI)
The ICS (either one) just has a contact closure.
The contact closes when the AUX ringer is told to ring. This can be via a phone or a phone line (you program it).
This closure is just a signal to your Nite Bell. It cannot supply Current to turn your nite bell on. It does not supply Ring current either.
Your nite bell has to be powered separately then this is just a signal usually closes a super lo current relay that will energize the higher voltage or current to ring your bell.