Pump Failure Indicator

This circuit is based on Dave Johnson's Bad Light Bulb Indicator circuit at http://www.discovercircuits.com/DJ-Circuits/bad-bulb.htm. I'm using a float switch in an underground 600 gallon rain water tank to shut off the 12V sump pump when the tank is empty. Because I only want 2 wires going to the sump pump I want to use this circuit back in the above-ground control circuitry. The pump draws 2.5A at 12V so the shunt resistor (R1) is sized for that. You will need to adjust R1 for the load you have.