Do it Yourself Wiring for a Square D Pressure Switch | Hunker Nov 29, 2018A 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 Wiring A Compressor Pressure Switch Kill the power to the compressor completely when you are wiring a compressor pressure switch. Basic pressure switch wiring. You have a power supply to the air compressor. For the typical DIY type home or small workshop air compressor, that power supply is a plug on a wire that connects to a wall socket.