Weird dual tank question...

[Chop]

I rebuilt the whole dual tank system in my truck...new right tank sending unit selector valve and selector switch in the dash...
It worked great for 2 weeks I put gas in the left tank Friday and tried To switch it from the right tank and it wouldn't switch.
On to today I have been working and haven't had a chance to look at the problem...I needed the battery from my truck so I swapped the battery out and did what I needed to do...I switched the tank to the left just messing with it while I had my battery out ... Well when I put my battery back in it switched and stayed on the left tank...... Anyone got any ideas on what's going on?

 

[Jims86]

I rebuilt the whole dual tank system in my truck...new right tank sending unit selector valve and selector switch in the dash...
It worked great for 2 weeks I put gas in the left tank Friday and tried To switch it from the right tank and it wouldn't switch.
On to today I have been working and haven't had a chance to look at the problem...I needed the battery from my truck so I swapped the battery out and did what I needed to do...I switched the tank to the left just messing with it while I had my battery out ... Well when I put my battery back in it switched and stayed on the left tank...... Anyone got any ideas on what's going on?

Gander at the wiring, and make sure nothing got pinched. Also, take the valve out and make sure nothing is mechanically sticking.

 

[fallguy]

Wiring

This is a wiring problem, most likely at the fuel tank selector valve setup on the passenger side underneath, as you know. I had that same wonky issue and was sure my setup was bullet proof and i traced all wires for the tanks finding nothing. I went to the selector valve armed with the wiring diagram...low and behold...one wire was handing on by a thread and the black tape was keeping it connected some of the time. I eliminated the crimp connectors and soldered everything into place.

Swear to God before settling in to the wiring diagram i too everything apart first...cost me many hours of screwin around.