The switch isn't the problem.. The plunger on the switch presses down on the shuttle spool in the valve... There is a groove cut into the spool that the tip of the switch plunger can sit into... Unless the shuttle spool is shifted to either side do to uneven brake pressure.. If/when the shuttle spool is shifted it blocks flluid flow to one side of the system... The theory being lower pressure means theres a leak so stop the fluid flow... However when you are trying to bleed the brakes it can block fluid flow for that operation as well... Usually it doesn't but yours may be...