[RMcNeal]

Thanks Dutch.
Actually there is only 1 wire that goes from the fresh tank to the panel read out. For my fresh tank, that's a blue 18 guage wire. The other wires are on the sensors on the tank itself, then a "sending unit" for lack of a better term, sets a resistance on the blue wire that indicates which sensor is closed, 1/3, 2/3 or full.
They used to work flawlessly on the fresh tank, but never worked on the black or gray after the first couple of uses.
In my case, I only use the fresh tank for a small amount of water on travel days for flushing and washing hands, and then in the winter when I cannot leave a hose outside. That's actually why I'm trying to get them working. When hunting season comes in November, I'll have to fill and use the fresh tank and my only water access is a long way away so knowing a rough level is very handy. There's typically several of us in the camper during that 2-3 weeks, so water gets used a lot, and my best guesses go out the window vs. when it's just me and my wife.