Dual fuel tanks and valves

My 1980 GMC 1 ton dually has dual fuel tanks on looking at the switch does anyone know which color wires or number goes to the left tank or the right tank? I'm trying to find information on how to troubleshoot the passenger side fuel tank has been replaced the driver's side has not been replaced yet but I have the new one, so for now I'm just running fuel out of the passenger side or I'm trying to. My son had this truck for a few years and he started fixing things and now he doesn't remember which wires go to what tank? Where the valve is it switches from one tank to the other, ? I would like help in trying to figure out if it's switched over to the right tank or not because right now it will not start the fuel pump doesn't seem to be pumping fuel into the filter so I bought a new fuel pump to change it because it's an old fuel pump and it's probably in need of being replaced anyway.

I forgot to mention the gas gauge stays in the full no matter where I position this switch

Either of these any use?

Thank you I will use these diagrams and see what I can find, my question too is where is this selector valve that switches the fuel from one tank to the other?

I have an 84 GMC C1500 with dual tanks. My switching valve is on the passenger side near the fuel tank. Follow the fuel lines coming out of each tank and it should lead you to the valve.
Mine has a heat/ dust shield covering it.

Copakekid said:

I have an 84 GMC C1500 with dual tanks. My switching valve is on the passenger side near the fuel tank. Follow the fuel lines coming out of each tank and it should lead you to the valve.
Mine has a heat/ dust shield covering it.

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Same on my ‘80 half ton, inside of the frame rail just in front of the back cab mount.

Here’s a picture without the bed on, ignore my hose routing (my valve was bypassed)

They’re all in the same spot. And if un fcked with, have a tin cover over it that is a challenge to get at all the bolts (but possible. Just a small jigsaw puzzle)

I had one tank on my 85 that would read way past full all the time. Turned out the ground wire was broken off from the sending unit. Once it was reconnected, the gauge reads correctly.

Here's a pic of the aforementioned shield.....can see the holes and get an idea where to hunt for bolts.

Doppleganger said:

Here's a pic of the aforementioned shield.....can see the holes and get an idea where to hunt for bolts.

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I’d like to see one mounted,

My truck never had one, or it was removed by the original owner, or Dad took it off and didn’t want to put it back.

CalSgt said:

I’d like to see one mounted,

My truck never had one, or it was removed by the original owner, or Dad took it off and didn’t want to put it back.

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Sans the rod.

Doppleganger said:

Sans the rod.

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Pretty!

Does the rod go to the bottom of the cab or what?

I made a shield out of scrap aluminum , but the stock one is so much nicer

CalSgt said:

Pretty!

Does the rod go to the bottom of the cab or what?

I made a shield out of scrap aluminum , but the stock one is so much nicer

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Best I could find with the rod. I'd get you a new pic but I left it off for the time being until the fuel lines are all connected. Rod goes from the edge of the shield to a 90* tab that attaches it to the frame.

Doppleganger said:

Either of these any use?

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The wires that come off my switch are pink pink with the white stripe light blue and green, there's a black wire hanging there but I don't know if it goes with it

Here is a photograph of the switch