Fuel gauge issue

[Jesse83]

Hey everyone, so I've been working on an 86 c20 and when I first it, it only had the passenger fuel tank but I decided to take it out and buy a new tank and sending unit (because the old tank and sending unit were absolutely trashed) and hook everything up on the drivers side. Bypassing the selector valve was easy as far as the hoses go but I cant get the electrical to work right, when the tank has 1/4tank of gas it reads at 1/8 and so on. Basically the entire gauge is compressed into half of it. The only thing that was done on the selector valve was taking the main wire that runs to it and running it to the tank instead of keeping it going to the selector valve and running the actual wire for the drive side to the tank. Also I know that the sending unit is grounded good. Anyone have any ideas as to why the gas gauge isn't working right? Sorry if that's all hard to understand, me and my dad have both worked on it so I'm just kinda putting all the bits and pieces together

 

[Bextreme04]

I'm confused by what you have done. Did you bypass the selector valve and have the fuel pump drawing from both tanks through a T or something? Did you hook the fuel gauge up to both sending units now? That would explain why the gauge is reading like that if you did. The sending unit works off of variable resistance to ground. If you have wired both sending units up to the gauge rather than having them switched, you will have half of the actual value shown on the gauge.

 

[Jesse83]

I'm confused by what you have done. Did you bypass the selector valve and have the fuel pump drawing from both tanks through a T or something? Did you hook the fuel gauge up to both sending units now? That would explain why the gauge is reading like that if you did. The sending unit works off of variable resistance to ground. If you have wired both sending units up to the gauge rather than having them switched, you will have half of the actual value shown on the gauge.

Yeah sorry I didn't quite know how to word it, but no I only have one tank on the truck (the driver side tank) and so the fuel pump is only pulling from that tank. My dad is the one who did the wiring aspect of bypassing the selector valve and the way that he explained it to me was that there is a main wire running into the selector valve and it splits inside of the valve and separates into two wires coming out. One for the the passenger and one for the drivers side. Well whenever we put the tank and sending unit on the truck he noticed that the wire running from the sending unit to the drivers side was messed up in multiple places so he decided to completely bypass the selector valve by running the main wire that goes into the valve, directly into the tank

 

[Bextreme04]

I'd have to look at my truck again, but I'm pretty sure that the sender wires go up to the dash switch on my 80 and don't go through the selector valve at all. The single wire to the selector valve is the power to activate the valve when the switch in the dash is activated.

 

[Jesse83]

I'd have to look at my truck again, but I'm pretty sure that the sender wires go up to the dash switch on my 80 and don't go through the selector valve at all. The single wire to the selector valve is the power to activate the valve when the switch in the dash is activated.

Oh that makes sense, yeah I believe he had said that it was the power wire that he ran directly to the sending unit. So the power wire going directly to the tank shouldn't cause the gauge to act up like that? So there's probably something wrong in the wires somewhere else

 

[Bextreme04]

If he moved the wire that went from the selector valve to the sending unit, it would not be good. He shouldn't have had to move anything near the sending unit or tank, just bypass the switch in the dash so that only the single wire to the one remaining tank goes to the single wire going to the gauge.

 

[1985c20]

I'm pretty sure the later switching valves handled the gauge side as well. The earlier ones only had a single wire to switch the valve but the later (80 or 82 on maybe?) had 5 or 6 wires so the sending unit readings went switched at the valve not at the dash switch. Maybe your dad just took the wrong wire from the valve. But I don't think the gauge would move with fuel level if the wiring was wrong. What brand sending unit did you install? Could just be cheap inaccurate china parts.

 

[AuroraGirl]

I'm pretty sure the later switching valves handled the gauge side as well. The earlier ones only had a single wire to switch the valve but the later (80 or 82 on maybe?) had 5 or 6 wires so the sending unit readings went switched at the valve not at the dash switch. Maybe your dad just took the wrong wire from the valve. But I don't think the gauge would move with fuel level if the wiring was wrong. What brand sending unit did you install? Could just be cheap inaccurate china parts.

I can check my 1980 for its wiring to the valve. its original.

 

[AuroraGirl]

only photo i have atm with valve. can check more later but I dont see much for electrical

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[AuroraGirl]

If he moved the wire that went from the selector valve to the sending unit, it would not be good. He shouldn't have had to move anything near the sending unit or tank, just bypass the switch in the dash so that only the single wire to the one remaining tank goes to the single wire going to the gauge.

do you know what these wires look like and where they run?