1973-1991 Dual fuel tank systems theory of operation

[MiniD]

It is not possible to wire it so the returns go to the "wrong" tank. The tank switch switches both the supply and return with the same signal. It is possible to wire it so that the wrong tank is selected but the supply should be coupled to the return.

Of course, there are ways to screw that up but they involve re-plumbing your fuel lines. Just re-wiring can't do that.