Do it Yourself Wiring for a Square D Pressure Switch | Hunker Sep 23, 2009A Square D pressure switch is a means of controlling pressure in a pump. Over time, the pressure switch can become worn out and need replacing. New Square D pressure switch installation also requires rewiring. If you are careful to follow safety procedures, this can be done at home.Author: Annie Walton Doyle How to Wire a Pressure Switch for a Water Pump | Hunker Without the use of the switch, the water pump would always be "on" or "off". However, with the pressure switch, the pump can be adjusted to turn "on" and "off" at predetermined settings to control the pump and subsequent pressure. By following a few basic procedures you can wire a pressure switch in a matter of minutes.