If you would like to know what the water level is in a tank from a remote position all you need is a few lengths of stainless steel wire or rods mounted in a rubber or cork cap; one long wire all the way to the bottom of the tank and all the others, as many as you like, at different length but parallel and not too far from each other.
Then you solder, crimp or screw a few coloured wires to each of all those stainless steel wires/rods that should be sticking up a bit above that rubber or cork cap, with the centre longest stainless steel wire going to earth/negative and all the others to a few LEDs mounted one above the other(and perhaps marked in either fractions or litres/gallons) in your living quarters with all their cathodes joined together and connected to +B via a momentarily on switch which when pressed will light up whichever LED/s if a path exists through the water in the tank.
Full tank equals all LEDs on; last wire touching the water equals one LED on.
I would advise you use ultrabright LEDs and you could also solder a 1k resistor (if using 12 volts) in series with each of those LEDs to prevent any damage to them if the stainless steel wires touch the earth wire accidentally during transport, although I didn't use them in the fresh water tank in my RV (I put plastic spacers between the stainless wires) and if you feel tempted to do away with that momentarily on switch to have the system operational all the time let me know what you know about constant electrolysis and potable water.
Now, does anybody know how I could use a similar setup to do away with my lousy and unreliable dashboard fuel gauge which I would love to replace with half a dozen LEDs?
What sort of plastic or non conductive tube (1.5" to 2.5") will stand being immersed in gasoline all the time and what sort of adhesive can I use to glue it to the tank float cap?
Is gasoline as conductive as non distilled water?
