Look under Zarzul here on the zone. He makes a nice probe. I believe it is now being sold under Wild Horse Innovations? Nice piece anyway. Try starting the probing routine on the 2800 and touching the 2 wires together if it stops it is right, if it never moves try initiating the probing sequence when the wires connected. The best way I believe is to have a normally open switch and if a wire breaks everything stops til you fix it. If it is normally closed it just keeps going. I too have a 2800 though I havent pulled it out of storage for a refit with Mach. Mine is complete less any way rs232 software or cards. On my Dyna lathe the limit switches were wired NC. I just had to change the setting in Mach. If I could find the exact replacement switches in NO, I would replace them but they do work well in all of my tests so far.