I have them on my Wood worker. I think when I first got the CNC I tried to pull them out but was unable to grab onto anything. I would probably cut/drill a hole the diameter of my cable into the plugs at both ends of the tube, then use my electrical wire pull rod to pull the cable through. You would need to have a bare cable for this to work.
If someone has removed the old light cable in the bicycle frame without knotting the new one to it, you can pull in a new cable by inserting a wool thread into one hole and sucking on the other hole with the vacuum cleaner until the wool thread comes out of there again. The new cable is then knotted to the wool thread and pulled in.
Oh wow! Thanks for all the replies! Thanks also to Onefinity!
I can do as suggested and simply drill through the plugs and pull the wire through. As I keep studying the problem, it turns out I may not need that sensor at the back. That is the subject for another thread though.
Great suggestions on using string and air pressure. That is how I clean the tubing on my water cooled computer. I blow a string through it and then tie on to my cleaning gauze.