Outer Limits 4x4 Board

I just replaced my fuel filter on my MK Nissan patrol 3.3TD. On the bottom of the fuel filter there is a drain plug that has some sort of sensor in it but the wire that runes to it was broken. Can someone please tell me what this sensor does and do I need it. Thanks alot.

IT is probably the water alarm.. when they get water in them a light or buzzer goes off inside the car.
thats what it is on may other diesels.