The sensors are on the side of the tank in question somewhere, generally in a more or less vertical line. There are little wires that connect to a smallish plastic blob thingy (a resistor pack) and a couple of wires from it that go to the display panel. (To be technically correct, the sensor probes go through the side of the tank; they're just metal stud contacts with some hardware to mount them in the tank wall.) Mine are next to where the black and gray tank drains are, and are plainly visible when the wet bay compartment door is opened.