[dmjlambert]

I made the fuse box diagram.

That schematic is pretty complicated and it took me a while to figure it out. It is very interesting. I was having trouble figuring out how a 3 port valve would be used to switch between 3 tanks, but I see now you use 2 of the valves. That is clever.

Do you think the valves draw power all the while the electricity is applied to them, or do they only draw power long enough to switch the valve to the desired position and then internally disconnect power and will stay in the switched position even with the 12V switched disconnected? I was wondering if using momentary contact switches would be feasible.

That is interesting about the return lines filling up the main tank. Is that applicable only to fuel pumps that have return lines? Mine is a 1969 truck and the fuel pump only has a port in from the tank and port out to the carburetor. So I suppose the setups with return line would be for those later trucks such as 71 and 72, is that right?

I have been thinking of using a brass valve down on the floor, and push a sheet aluminum arm with a hole in it onto the rotating shaft and put a dob of glue to hold it to the shaft, and glue a magnet on the end of the arm, and then position 3 reed switches at the 3 positions the arm points to when you select a tank, in order to switch the sender signals to the gas gauge.

I would bet that switch could be enclosed in a plastic box or large pill bottle, or even wrap it in a baggie, and the contacts could be treated with some bulb grease, to make it automotive and dust friendly.