If you put the Micropulse in monitor mode do the the grey and black tanks show green? With the panel turned off press the power and status buttons at the same time. All lights should turn green. Then press the status button once. The three tanks should show green. If any are yellow then the sensor is defective or there is a bad connection.
On my 2008 Classic 25fb under the fridge where the water pump is located the monitor sensor wires come up from the tanks and the sensor wire from the panel are joined together with a RJ-11 connector. This allows the tank sensors to be disconnected without cutting the wires. The sensors on the tanks are located close to the dump valves of the waste tanks and the drain of the water tank which in my case is on the street side of the trailer. The monitor panel is located on the curb kitchen wall. The wires are run under the subfloor via the subfloor chase.
When I calibrate my tanks I usually disconnect the tanks I don't want calibrated. One tank will go crazy occasionally. Recalibration seems to correct it for the season. I use an inline water meter to measure how much water I put in the tank for the empty and full readings.
2008 Classic 25fb "Silver Mistress"
2015 Ram 2500 6.7L Cummins. Crew Cab, 4x4, Silver
2010 Tundra 5.7L, Double Cab, 2wd, White