You have a source device so your PLC should be sink input.
Did you tie the GND to your PLC common?
with the load resistors in place, you should get a high to low reading on the sensors without any connection to the PLC.
Monitor with a voltmeter between common and Yellow, by turning the motor etc as slow as possible, before connecting to PLC.
If you turn slow enough you should be able to read a 24v to 0 transition, too fast and it will be anywhere in between.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.