The tank selector valve should have 3 nipples to connect fuel lines to. One is right tank, the other is left tank and the only one left goes to the fuel pulse pump.
Remove and disconnect the fuel selector valve, confirm there is fuel flow from each tank feed line with selector valve removed.
These valves often had the ability to turn a full 360 degrees on the center stem when not bolted down. It needs to be unbolted too "clock' the center stem, so the middle is the off position. Place the end of the fuel line going to the pulse pump into a clear jar to check for fuel flow.
From there move the tank selector valve stem to determine where right tank flows, then back to where the left tank flows. Off should be in the middle.