A float switch prevents flooding. An air conditioner includes a normally closed float switch, which turns off the system if the condensate drain clogs and water overfills the drip pan. A bilge or sump pump has a normally open float switch, which turns on the pump when the water level rises above a set point. A float switch's wires connect in series with the appliance's control circuit. Power flows to the appliance when the float switch closes, and the appliance turns off when the float switch opens.
Turn off the power to the appliance the float switch protects. If the float switch operates in an air conditioner's drain line, then turn off the air conditioner circuit beaker displaying a "furnace" or "air handler" label. If the float switch operates a pump, then either unplug the pump from its wall outlet or turn off the appropriate circuit breaker.
Remove 3/8 inch of insulation from the two float switch leads and the two wires to which the float switch connects. Use wire strippers for that task.
Twist the end of one float switch lead around the end of the wire that connects to the power source. Then cover them with a wire nut. If the float switch protects an air-conditioning system, disconnect the furnace's transformer wire that connects to the red thermostat wire, and then connect the float switch lead to the transformer's wire. If the float switch operates a pump, connect the lead to the wall outlet's plug wire or the wire connected to the circuit breaker.
Twist the end of the second float switch lead to the appliance's load wire. Then screw a wire nut over the ends of the wires. If the float switch protects an air-conditioning system, twist the float switch lead around the thermostat's red wire. If the float switch operates a sump pump or bilge pump, wrap the second float switch lead around the wire that connects to the pump motor.