Phil,
Thanks for your thoughts. The problem is that the sending unit is grounded to the cab. That is to say the body of the sending unit as well as the post that the sending unit wire lands on are both grounded to the tank, cab, and negative side of the battery. When the unit is not installed (none of the 5 screws in place) in the tank it works correctly. A puzzling situation.
At anyrate; Yeah my truck is a 1948. It has been in the family since 1979 & had two tanks when we got it. Looking at things, my best guess (emphasis on "best" and "guess") is that the tank under the bed is stock and the tank in the cab was added by someone. The fuel gauge reads the tank under the bed. The cab tank was never metered. I am adding that function and currently have it hooked up to the fuel gauge. There is a valve near the passenger's feet that selects which tank is in use.
I sorta like the 2 tank system. Have never seen another Advanced Design Truck that has 2 tanks.
Joe
