I cannot remember if it is this forum where someone asked about a low water sensor for a Disco and I suggested using a 91 Range Rover tank cap.
Well its a little more complex.
The reed switch is always closed and when empty becomes open or "off"
So you would need to use a Normally open relay which closes power off,. An AB relay would be fine.
On a rangie it is interpreted by The" Dash controller' 145 on the diagram and it flashes after a time delay to stop falses.
One more thing to go wrong AND I learned about the time delay. Not good if a hose bursts.
Regards Philip A