Hi all. Long story short I am rewiring a friends toy hauler following an incident with an angry dog getting into his side yard and chewing up all the electrical on the bottom side of the trailer. I've rewired everything so far with the exception of the clean/grey/black water tank sending units and I need some insight. A generic image which I found online of the tank gauge set up that is on the trailer is pictured below. On the bottom side of the trailer, each of the tanks has four studs sticking out of the side for the sending unit wiring, twelve studs total between the three tanks. The studs are arranged in two banks so to speak, one stud on the bottom left of each tank and three studs stacked vertically on the right bank, each about 4"s higher than the one below it. I found four wires coming through the floor which I am assuming are the wires back to the gauges but unfortunately cannot confirm this without a major overhaul to the cabinets and interior of the trailer. From what I have read, sending units of this style rely on the fluid in the tanks to conduct electricity. If my understanding is correct is it safe to assume that each of the lower left studs could be a ground wire and each of the other three studs per tank would be fed by one of my other remaining three mystery wires? One wire per tank, wired in parallel to the three right bank studs? Please excuse my ignorance and thanks in advance for any input. The plan is to head back out to the town my friends trailer is in this weekend to test the four wires I have to hopefully get the tank gauges back in working order.