It's an old thread now, but I managed to sort it with a great result, cheers Dave.
I wish I had seen this before heading down my path I am on. Although mine doesn't seem like its going to be bad. There is a company that sells a 3 port selector switch to wire off my dash switch. My truck is 87 with the former TBI that I am swapping out now to carb. Was going to just use the pressure regulator and motor on. But one pump in tank quit. I am taking out the 6 way valve for the 3. Putting in a electric pump just in front of that selector. The pump I am running through the oil pressure switch and the fuel pump relay so I can completely eliminate the computer and all the sensors. Since mine is a TH400 I don't need to computer. Your use of the relays seems to be a good stream line approach with two pumps. You are right. Not only dual tanks but two pumps if one fails. My luck the pump that fails is the one with the full tank of fuel! And the good is the one I just ran nearly empty!
