Originally Posted by Herk7769
This has been explained previously, but from the responses it looks like it could use a refresher.
The system uses 4 metal buttons that are installed by the factory in a convenient side of a more or less rectangular plastic tank. (see photo)
One is located on as close to the bottom as possible without hitting a seam and is connected to the system's ground wire.
Another is located about the same place on the tank vertically and although it is supposed to indicate 1/3 full on the monitor is really a "not empty" light.
The next one up is about 1/2 way up the tank wall and is the 2/3 full light, but indicates about 1/2 full.
The last is located about 7/8 the way up the wall and when the liquid level hits that, the tank indicates full.
Now, having said that, the levels only indicate the above when the tank is LEVEL. Any tilt to the tank will affect how the monitor reads when the button gets submerged.
If the tank is tilted away from the buttons, the tank may be "full" (not able to accept more liquid) while the middle indicator button only shows 2/3.
Conversely, when tilted towards the buttons, the tank may indicate full even though the tank can accept a lot more.
I attached the wiring diagram and troubleshooting guide if you are having issues.
I don't remember which camper it was at the moment. But our sensors were just sheet metal screws into the plastic with some sealant around them. If you ever wondered why they were always reading full, it was because the sharp pointy end was about 3/4 of an inch into the tank. No amount of flushing would clean them off.