3 tank probes; 2 lights

[Chuck]

tearing out my bathroom, I noticed that my black tank has 3 probes. The control panel only has 2 lights for indicators. "1/2", and "full".
(I think they're actually labeled "2/4", and "4/4").

So what is the 3rd wire for? I figured there'd only be 2 probes--one for each panel light.

(and I've also had the idea that I could use these wires to attach to a new black and previously non-existent grey tank, since they're already fished up through the walls to the front of the trailer, where the control panel is).

[Chuck]

so, nobody can explain the how the circuitry of a conventional tank probe/level gauge system works?

[Ag&Au]

Originally Posted by Chuck

so, nobody can explain the how the circuitry of a conventional tank probe/level gauge system works?

The most likely scenario is one common probe, and two sensing probes. the common probe would be the lowest.


When the tank fluid reaches the second lowest probe, a small current would be allowed to flow between the lowest and second lowest probe due to the impurities in the water. The indicator circuitry would sense this and light the half full light. The same thing would happen when the fluid reached the highest probe and the full light would illuminate.

Ken