New rig, could use some troubleshooting advice.

Your Fuel Tank Selector feature should be wired something like this:
If your system has a Return Line from the Carburetor back to the Tank(s), you have a Six Port Tank Select Valve.

From Tank 1 with Pressure and Return = 2 ports

From Tank 2 with Pressure and Return = 2 ports

To and From Engine with Pressure and Return = 2 ports

That's six fuel line connections at the Selector.

Pix and Discussion Here

This is a Replacement Six Port Select Valve