CNC mill home sensor question

I got a CNC mill on Monday that has a dead controller. It's a Denford
Easimill 3 and I'm going to use a Campbell Combo breakout board and
Mach3 to control it. I spent most of yesterday and today removing the
bits that won't be re-used (computer, screen, relays, etc.) and
figuring out the pinouts for everything that is being re-used (stepper
controllers, limit switches, motors, etc.). I have a question about
the switches that set the origin on each axis. This machine has the
type that looks like a small spark-plug and registers when it
appraoches a small steel block. They have two very small wires coming
out of them.

How do these switches work? Do they need a circuit to run them, or
can they act like cherry switches with a conventional hookup? This is
my first CNC project, I appreciate any help.

cheers,
c