The residue on the walls is causing the black tank to read wrong you could try leaving about 10 gals of water in it with or without some tank cleaner when you depart for your next stay and let it slosh during the drive that my clean things up. more then likely the gray has had a ground come loose may require dropping the underbelly to get at the wires.
Jake my sidekick (yellow Lab)
2017 RAM 2500 CC 4X4 Cummins Diesel
2016 Flagstaff 26 FKWS
AF&AM & El Korah Shrine of Idaho