A portable fluid monitoring controller tester system for fluid monitoring equipment includes a control panel, electrical interfaces, and associated circuitry for simulating the fluid overfill sensors and other features of a trailer. The tester is a self-contained device that meets or exceeds various safety standards applicable to operating in an explosive environment. The tester may be powered, at least partially, by the fluid monitoring controller to which it is connected or from another power source, such as a battery. The tester has intrinsically safe outputs, and is configured to simulate different types of sensor systems found in fuel tanker trailers, including 2-Wire Optical, 5-Wire Optical, and Thermistor sensors. The tester is further configured to simulate ground circuits and the truck identification module (T.I.M.) of the fuel tanker trailer. The tester includes an enclosure that is impact and temperature resilient, and provides protection against windblown dust, rain and splashing water.