I can manually switch pump on but shouldn't pump be running ?I'm thinking switch is bad

What is the tank pressure. Can you hear the switch click. Is pump running?

Replace the switch AND the little pipe leading to it. Switches are cheap. You are correct in thinking that the switch should work on its own.

Assuming that when you use water, the switch does not turn on (audible click) the pump and pressure just dribbles down to nothing.

Before anything else is done I would take that little pipe and check it for blockage, Let men know what you find. Good luck. Tom