moparx12 wrote: They are NPN type NC switches.
Yes, you can use 1 pin,
But, you will need to wire them in series (serial in the linked image) (if they are in parallel it will not be possible to see if the circuit is broken until all three are open circuit)
[how do you get an NPN "switch"?? ... proximity sensor yes, optical sensor yes, switch [implies mechanical] no]