Re: Indicator Lights
On the waste water and fresh water tanks, there is an adjustment for them which is located behind the display panel's face plate. If you carefully remove that face plate, near each of the displays there should be a very small potentiometer which is the adjustment. While your waste tanks could be in need of cleaning, but the fresh water tank should be accurate, if adjusted properly. I would start with the tank either full, or empty.
Adjust the potentiometer to where the indication is proper, but such that it just goes to that indication, from the direction of the mid-point of the indication. In other words, if the tank is empty, turn the pot to where it says 1/4 and then back off to where it just starts to read empty. If you start with the tank full, adjust to 3/4 and then to where it is just indicating full.
Once that is complete, adjust the level to where it is 1/2 and fine tune it for accuracy, then go to empty/full and adjust again. Make full and empty accurate as they are the most important. For waste water the process is the same, but it is more difficult to do since you can usually look at your fresh water tank and see where the actual level is. When I did my waste water tanks, I knew the total volume of each tank and so began with the tank empty, then adjusted the level with a 5 gallon bucket as a measure.
Also with waste tanks, any residue that is left behind will effect the accuracy and that will probably cause it to vary from time to time. Some folks put a great deal of time, money and effort into keeping the waste tank levels accurate but because the manufacturers use some of the cheapest type of level indicators, most RVs are of fair accuracy at best. The quality of the tank indicators does vary quite widely. Some can be pretty accurate, others are useless. Most fulltimers soon get to where they know how long the tanks will last and only use the display as a general indication, if at all.
There are better quality tank level indicator systems available but they are also fairly expensive. Typically the cost to purchase one is between $300 & $500 and if you get it installed the price will depend on the ease of getting access to your tanks. The cheap ones just measure resistance between electric points which extend inside the tank wall. The good ones use a capacitance probe method that can be very accurate and last for a long time. Such systems were developed for use in submarines and we only needed to do level indication adjustments to them once each year, back in the 60's. But they can also be quite expensive and so are seldom used.