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Thread: 1986 1/2 ton wiring

  1. #1
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    Cool 1986 1/2 ton wiring

    I need fuel tank to gauge wiring diagram with dual tanks

  2. #2
    Senior Moderator chevychase's Avatar
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    Is yours carb or tbi.

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    Senior Moderator chevychase's Avatar
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    dual tank wiring - The 1947 - Present Chevrolet & GMC Truck Message Board Network this is what i could find . On your truck it was a option .
    Searched a quit few places all said it was a option did not have diagram. I hate going too other forums but.

  4. #4
    Forum Moderator Boudin's Avatar
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    Here is the wiring diagram that is in the back of my shop manual. I have an 84 with the dual tanks.


    http://i89.photobucket.com/albums/k2...chematic-1.jpg


    Is there anything in particular you need it for? I have replaced both tanks on my truck as well as the solenoid selector switch and the dash switch. The dual tank setup is nice to have....but can be a pain.

    Hope this helps.

  5. #5
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    Welcome to the forum broncodw.

    There are a number of threads on this forum
    that have talked about this before, good resource.
    A quick way to find them would be *tag* searches
    but they can be found through regular searches too.

    I know 84, 86, and 87 are there because I posted them.
    Here's a post with some of the threads listed for you.
    http://www.truckforum.org/forums/che...tml#post130426

    Quick tips since you did not say what the problem was:
    If gauge is sitting mid-range, likely fuse or hot-to-guage problem.
    If guage is pegged to full side, look first that the connector on
    single wire coming from valve to guage is not loose.
    That usually under cab under driver.
    If guage is pegged on empty, look for that same wire shorted to something.

    Above assumes same problem no matter which tank is selected.
    If only on one tank, inspect wire between the valve and bad tank.
    Not likely that valve only fails on guage function wth gas still flowing,
    unless the selector is not actually working for anything
    and the gas comes from same side when switch is either side.

    Hope that helps, be sure and post back an update for us.
    That's how this place becomes a goldmine for info.

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    thanks for the info I'm having guage problems just got truck one tank is new the other needs replacing but for now I want the fuel gauge to work so I won't walk was told it gets terrible gas milage and don't trust it It has a crate 350 with roller cam and lifters Is fast 650 dual holly ai will use all the info and let you know the details

  7. #7
    Senior Moderator chevychase's Avatar
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    Thanks and welcome. I hate not having fuel gauge work. Pain too figure out.
    Check all your grounds are good.

  8. #8
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    Worse than walking because the guage fooled you,
    is walking while you still have gas.

    You need to make sure the wires to that fuel switching valve are good,
    and that it's not the cause of the guage problems.
    When you switch tanks on dash, the internals of the valve switch the guage.
    The dash switch is not wired into the guage itself nor the senders in tanks.
    It just controls who's connected.

    It selects which pipes and separately which sender.
    In Boudin's drawing you see the two switch wires at *top*
    and the guage and sender wires are *bottom* three.
    The dash operates the valve to change pipes.
    The valve operates an internal switch to change senders.

    Works the same for both mechanical (eng) and electrical (tank) pump setups.
    Just two more wires are added if using in-tank pumps.

    LOL you still didn't say what's wrong with guage, how it's acting.
    Last edited by crabtruck; 12-01-2010 at 01:39 AM.

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    On the left tank the guage reads on the empty line although the tank is full on the right tank, the guage pegs past full almost to the 4 o'clock position the right tank is old and needs replacing the left tank is new

  10. #10
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    Generally for *pegged* fuel guages,
    Full is telling you sender wire is broken,
    and Empty is telling you to look for the sender wire to be shorted
    along the way between tank and guage.

    With dual tanks having both conditions, one each tank,
    I would look first for a miswire/patch job at selector valve.
    Could be other things but start easy: like is it plugged in ?

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