What is wrong with my plumbing. Replaced all pipes, bladder tank, fittings. New switch 20/40. Tank holds at 45psi. Switch won't come on auto.. and I have to hold the lever to get the pump going. Release, the pump stops. I havewate when pump is on. Olds pressure about 30 secs then drops.

Something is blocking the piping to the pressure switch.

I havewate when pump is on. Holds pressure about 30 secs then drops.

Are you saying that when no water is being used, it hold pressure for thirty seconds and then drops to zero? If so, then you have a footvalve/checkvalve problem. And that would explain your switch problem. Your switch is designed to shut down when pressure drops to ten pounds or more below cut in pressure. That is to prevent running the pump when the well is dry. That would be why you have to hold the reset lever to get the pump running again.

Sound reasonable? Otherwise, I will vote with HK.