I'm trying to get information right now about the sensing system itself, but the general idea of the propane sensor is that there is an electronic component, called a potentiometer (a variable resistor) mounted atop the mechanical LP gas gauge at the tank. As the float in the LP tank changes level, it moves the mechanical indicator shaft on the gauge. The potentiometer is linked to that shaft, and as the mechanical gauge shaft rotates, the potentiometer provides a variable DC signal, proportional to rotation, to the indicator panel. It works somewhat like an audio volume control. My first guess would be a broken wire, either between the panel and the gauge, or maybe a bad connection right at the gauge connection or the panel connection.