Not certain but I assume one lead is a low voltage supply and the other three relate to each third of the tank water level. If it is like my tank the sensors are stainless steel rods and the on-board electronics reads the capacitive value between each rod where there is water and this gives the level in the tank.
These rods become oxidised over time and give false or zero readings and need cleaning. Can you remove the sensor from the tank and clean it, also if you have been moving the connections about have you connected them wrong hence the red light warning?
As for voltage and power requirements check with a voltmeter between each contact on the PCB at the panel end for a voltage, may be 12 or 5 volts (most likely) Once you identify the feed it should be possible to work out 1/3, 2/3, and 3/3 - but if you can get the sensor out of the tank these should also correspond directly to the water level in the tank.
Last edited by torwood; 16-06-2017 at 16:37.
Motorhoming with cats and wife - all equally mad!