The landing gear failed to retract on my 1994 M20J. I removed the belly panel and exercised the up limit switch several times and thereafter it worked again. The switch comprises two components: A micro switch and a plunger. The plunger is spring loaded and I noticed that it was a little sluggish to reset when I removed it so I cleaned it and lubed it with some silicone spray. The problem may have been mechanical or there may have been a problem with the switch, but I replaced the switch anyway.