Fuel Line Diagram Dual Tanks

[Spline64]

Hello,

Looking for a fuel line diagram for a 73 GMC C2500 pickup with a 7.4 ltr. and dual tanks.
Currently the entire system has been bypassed. Previous owner installed a 350 and was only using one tank with an electronic fuel pump direct feed to the carb.

I have since put a 454 back in and am in the process of trying to make things stock-ish with the dual tanks and a mechanical fuel pump.

I did find some electrical diagrams on this forum (thanks guys!!) but can't seem to find how to connect the fuel pump lines from both tanks to the mechanical pump.

Thanks in advance,
Pat

[Desert1957]

[Dead Parrot]

Not a diagram but on my non-emission 75, there is a single steel fuel line that runs from the tank switch valve to near the mechanical fuel pump. The tank switch valve is located on the passenger side between the tanks. It has two lines in and one out. There are no return lines, the tanks just vent to open air via small plastic things off the sender units. A short length of 3/8 fuel hose connects between the output of the valve and steel fuel line. Longer 3/8 fuel hose connects to the tanks from the inputs on the switch valve. A single wire connects to the switch valve and goes to the select switch in the cab. There are two more wires from the cab switch that go to each tank sending unit for the gauge connection. One per tank.

[ray_mcavoy]

Dad's 77 has a similar setup to what Dead Parrot just described. It too is a non-emissions truck with plastic vent caps on each sending unit that vent the tanks to the open air.

The only difference is that it has an additional 1/4" return line running from the fuel pump back to the switching valve and then back to each tank. It basically runs parallel to the 3/8" feed line. I believe the return line was used with certain engines to help prevent vapor lock (Dad's truck has the RPO LF4 400 small block).

Here's a pic of the switching valve with the lines labeled:

[Spline64]

Thanks so much guys!

Tank switch valve was nowhere to be found on this truck. After I purchase one, I've got the info to hook it up now.

Thanks again,
Pat