Turn off the power to the circuit that feeds the pressure switch.
Open the panel on the pressure switch to expose the black and white wires inside.
Feed the incoming power cable from the house into the switch body and clamp it in place with the clamp inside.
Strip the jacket of the cable back using the wire strippers to separate the three wires inside the cable.
Strip 1 inch of insulation from each of the wires using the wire strippers.
Twist the black wire around the black wire from the switch using a wire nut.
Twist the white wire around the white wire from the switch, also using a wire nut.
Wrap the bare copper ground wire from the cable onto the green screw located on the inside wall of the switch body. Tighten the screw with a screwdriver to secure it.
Replace the front panel of the switch.
Turn the power back on to the circuit.