Even though there are 4 buttons/lights on your panel, there is only 3 tanks. Those panels are generically built to suit needs in any RV. Sometimes a camper will have only 2 tanks, but 4 light.
As stated above, those sensor are pretty much worthless. Unless the camper is brand new, they almost never work correct. Crud and "stuff" and gunk and munk get caught on the sensors inside the tanks and create false readings. So, you are really best to just ignore those sensors and learn the signs when it's time to dump. The sound of the water hitting the tank when you flush the toilet, and a feeling for how much water you are showering with or how much you are using for washing dishes. This takes some time and practice to figure out.
We never, ever hook up the garden hose and leave the shore water turned on. We always fill the fresh water tank and then disconnect the hose. Knowing the amount of water the fresh water tank holds helps to know how much water is being used and added to the waste holding tanks. Also, if you dump your waste using a sewer "tote" at sights that do not have full hook-up, you learn real fast how much water capacity you have in your holding tanks. Between all of this, you simply learn when and how often to dump the tanks. Sound is key. Paying attention to water usage is another.
If you are hooked up to shore water but do not have sewer at the site, then a garden hose water meter is a tremendous help for monitoring your water usage. There are a number of way you can keep track of your actual water usage. Still, trial and error, and due diligence, and paying attention is what you need to do. You don't need the faulty monitor on the wall at all.
