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Help with fuel gauge wiring

Discussion in 'Tech Discussion' started by 77Jay81, Mar 30, 2014.

  1. 77Jay81

    77Jay81 Junior Member

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    Truck Year:
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    Engine Size:
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    Hi, I have a 1977 Chevy K20 that had twin fuel tanks. I am restoring the truck and am only running one tank. The wiring was a disaster and I'm trying to find out where the wire from the sending unit connects in the dash. To a wire at the firewall connector, to a wire in the dash? Any help would be appreciated!
     
  2. abe

    abe Junior Member

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    Did you ever figure this out? I was wondering the same thing since somebody else did a single tank swap and didn't wire it up
     
  3. Boone83K10

    Boone83K10 Full Access Member

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    neither...

    here is a wiring diagram for you.

    77_DualTankWiring.jpg
     
  4. T0G

    T0G Junior Member

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    Fuel Gauge Wiring.

    Hey, so i've got the same truck here, and im working on setting up a new, high pressure fuel system in the dual tank setup.
    All the other wiring is completed, but i cannot find where the fuel gauge wire is, coming out from the firewall.
    Originally, as shown by your diagram, the two signals (from each sending unit on each fuel tank) went through the firewall with the four prong connector, and sent one signal back out through the firewall connector, to the fuel gauge wire, back through another firewall connector (this is what im looking for), then to the gauge.

    for reference, i've taken and highlighted the wire i am looking for on the diagram you supplied.
     

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  5. Boone83K10

    Boone83K10 Full Access Member

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    You are reading the diagram wrong. That says "front of dash"...not firewall. The fuel gauge wire never comes out from under the dash. It goes from the control switch up to the back of the gauge cluster.

    The early models that had dual tanks did the electrical switching for fuel reading at the switch unlike later models such as mine that switched electrically at the selector valve. The solenoid is strictly mechanical in your truck. 30C and 30B feed into the back of control switch, that switches the signal that feeds to 30A aka the fuel gauge wire. It should be pink or red.
     
  6. Boone83K10

    Boone83K10 Full Access Member

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    Well I may be mistaken on that it doesn't come back out. Every diagram I see for the old setup says it comes out. I would follow the pink wire from the back of the control switch, see where it goes. It should lead you to the fuel gauge or it's been cut. The trucks are known to be hacked up, no telling what an owner before you did.
     
  7. T0G

    T0G Junior Member

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    It must come through the firewall, if the Fuel Gauge wire goes through that four pin connector.
    The wiring was stock, all modifications were done either by me, or my father (who was the previous owner). I'm going to look for a diagram that shows the fuse box exterior (engine bay side) and see if i can go from there.
    Currently i have my pink wire (new, installed by me) from the output of the fuel selector solenoid connected to the wire that goes through Pin A of the firewall connection. The wire was cut, and connected. I'm trying to find where the other side (going TO the gauge itself) is at so i can change the connection to it.
    I am no longer using the old style switch, and have the switch/fuel selector solenoid/pump set up all configured correctly, so that is no issue. I simply repurposed the firewall connector to give the proper connections to the new switch, and the A pin on the Firewall connector is no longer used inside the cab. I mistakenly attached my pink wire to that A wire, instead of to the gauge wire.

    If you happen to know the position of the Fuel Gauge wire coming from the engine bay side of the fuse box, that would be excellent as that is all i'm currently looking for.

    Thanks.
     
  8. Boone83K10

    Boone83K10 Full Access Member

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    apparently they wired them 3 different ways..

    here is two more ways..
     

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  9. T0G

    T0G Junior Member

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    Looks to me like the first picture you posted is the way the wiring is on my truck.
    I'll look for the fuse box diagram later.
    Is there a website you're looking at, or do you have a book of your own?
     
  10. Boone83K10

    Boone83K10 Full Access Member

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    why in the hell would GM take a wire from the fuse panel, out to the engine bay then back in to a switch then come back out to the engine bay to go back in to the gauge cluster.... they were high or something.
     
  11. T0G

    T0G Junior Member

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    Okay. SO.
    Chevrolet must have been high as a kite when they wired these things.
    The Fuel Gauge wire does not do a simple loop from the 4 Prong Fire-Wall connector, to the bulkhead connector.
    Oh no, that would be much too simple.
    What they DID do, was run the wire from the Bulkhead connector, behind the engine, down past the starter, down along the passenger side frame rail, to the old selector solenoid where it would then be spliced into the wire that comes from the four prong Fire-Wall connector, which makes its way back up the driver's side frame rail, to the 4 prong Fire-Wall connector, then inside the cab to the fuel selector switch.
    It's just a big-ol roundabout for no reason whatsoever.
     

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