Check the screw terminals. These terminals are exclusively used for the float switch and should not be connected to an external power source. Connecting the terminals to an external power source could damage the system.
Check the alarm circuits for continuity if the power light is off while the alarm is plugged in. Disconnect the power from the alarm. Attach a volt meter to the flat plug terminals. If the volt meter indicates no continuity, return the alarm to the manufacturer.
Check the float switch if the warning light and alarm horn are off while the float switch is turned on. Inspect the alarm system power cord for damage. Confirm that nothing is obstructing the float switch from moving and inspect the float switch cable for any damage. Replace any damaged cords or float switch.