Tank Monitor panel indicates when a wastewater holding tank is almost full. This monitor helps prevent damage to the boat that can happen because of accidental overfilling of the holding tank. When the red light is activated on the indicator panel, it indicates a full tank and operation of any fixtures connected to the holding tank should stop until it is emptied. The probe installs in a 1-1/4" opening on the top of the holding tank. As the content level rises, the float switch is pushed up until it activates the Full Tank light on the panel. Panel measures 3-1/4" x 2". Volts 12/24