Abstract: The over-fill monitoring system monitors the liquid level of a container as its being filled and visually indicates that the fill process should be stopped, thereby reducing the chance of over-filling and overflow spills. The over-fill monitoring system includes a fuel probe, a visual “fill limit” indicator, and an electronic control unit. The control unit is responsive to the fuel probe and activates the “fill limit” indicator during the fueling process when the fuel level within the tank reaches a predetermined “fuel fill” level. The control circuitry of the control unit also includes a “shut-down” timer, which deactivates the indicator light after a set period of time to prevent the control unit from drawing power from the battery.