Question about fuel gauge wiring.

Electrical and Ignition

  1. 73 Duster 360

    73 Duster 360 Well-Known Member

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    Hey guys I've been trying to get my fuel gauge working for a few months (one weekend at a time) and have gone through the entire system starting back at the tank

    The car now has:
    A brand new fuel tank.
    Brand New sending unit which is ground to the frame.
    A brand new mechanical fuel pump
    New rubber hoses at every connection point.
    Brand New fuel gauge.
    Brand new voltage limiter.

    I also made a point if flushing the steel fuel lines when I was replacing the tank. Problem is the gauge still doesn't move. At all.

    When reading other threads on here I saw someone say that the wire with the angled connector on the sending unit goes straight to the fuel gauge but when I took out my instrument cluster there were no wires connected to the gauge at all.

    When I got the car there was an after market fuel gauge mounted to the bottom of the dash with a tangle of wires all spliced into each other that came from a cluster behind the left kick panel. That gauge never worked either.

    My question is should there be a wire connected to the back of the fuel gauge in the instrument cluster? And if so where does that wire feed in from?

    My assumption when I took it apart was that the wire from the sending uniting ended up in the loom connected to the back of the instrument cluster and that the gauge received the signal via the circuit board.

    I have a physical manual but the diagrams are a bit confusing when comparing to actual locations within the vehicle. Any help would be appreciated.
     
  2. toolmanmike

    toolmanmike Moderator Staff Member FABO Gold Member

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    Ground the power wire that plugs into the sender and the gauge should go to full. You test the wire, gauge and cluster circuit that way. If it doesn't it probably needs a gauge.
     
  3. 73 Duster 360

    73 Duster 360 Well-Known Member

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    Since I already replaced the gauge would no movement mean I need to replace the wire?
     
  4. shittyslant6

    shittyslant6 Well-Known Member

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    well, I just went out and looked at mine, (it is a 70, but it should not change from 70 to 73) and there are no wires hooked to the fuel "gauge" in the cluster.
    PXL_20211121_014701633.jpg
     
  5. toolmanmike

    toolmanmike Moderator Staff Member FABO Gold Member

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    It could be if the gauge is new.
     
  6. shittyslant6

    shittyslant6 Well-Known Member

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    can't helpo yo
    can't help you beyond that. I'm not too good at wiring stuff.
    My fuel gauge is shaking the car and listening for sloshing in the tank.:lol:
     
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    • shittyslant6

      shittyslant6 Well-Known Member

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      • 73 Duster 360

        73 Duster 360 Well-Known Member

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        Thank you. That helps. So I have a disconnect somewhere between the circuit and the sending unit.
         
      • shittyslant6

        shittyslant6 Well-Known Member

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        that is my only guess.
        everything but the wiring is new. (that does not hold too much weight anymore considering the quality of parts but eh.)
         
      • 73 Duster 360

        73 Duster 360 Well-Known Member

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        So does anyone know where the power wire from the sending unit enters the dash? I assume it's one of the many connectors that plug into the back of the instrument cluster in that circular loom? If I can find both ends I can test for continuity in the wire.
         
      • 66fyssh

        66fyssh Don't Stop Believin' FABO Gold Member

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        Search for a wiring diagram for your car. Mymopar.com had them but they recently revamped the site and I haven't been on much since.

        I don't know about the 73, perhaps there is a trace on the circuit board that connects when you cinch down the nut. That's how the 66 fuel gauge gets power and ground.
         
      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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        First thing you need if you don't have, is go over to MyMopar and download the 2-volume 73 service manual. I believe it's Dodge, not Plymouth

        "The wiring path". from ground--to the tank sender---through the sender---out the wire, which goes up into the trunk, up forward in the left kick panel, and there' s a mating connector there for the rear harness. The tail/ turn/stop/ courtesy lamp wiring, backup lamps, and sender wire is in there.

        From the kick panel goes up into the instrument wiring harness and goes to the cluster via the multi pin connector(s) which attaches to the circuit board for the cluster

        The board traces convey the sender to one of the studs of the gauge.

        The gauge is powered by the (various names) IVR, instrument voltage regulator or limiter

        if the temp gauge works the limiter is likely OK

        AS MENTIONED do a quick test by grounding the sender wire. if that (key on) does not send the gauge to the high side peg, now you get to troubleshoot.

        Reconnect the sender wire. Acces the left kick panel and (using the diagrams) find the sender wire. Check that "to ground". It should read less if tank is full, more towards empty. The sender goes from about 23--to about 73 ohms or so. IF YOU READ in that range, consider the tank ground, wiring, sender, etc, OK to that point

        Next I would drop the column and pull the cluster

        REMOVE battery ground

        Generally if column shift, you must disconnect the shifter, loosen the clamp/ plate on the floor, turn the wheels so the flex coupler will move / angle enough, and remove the trim under the column, and the nuts (and one bolt some years) up under the column Drop the column down in the seat.

        Now pull cluster mount screws, and reach up in and undo speedo cable, and at some point the two nut connections for the ammeter.

        At that point you should be able to tip the cluster down and out toward you, gently work wiith the wiring to get a bit of slack, and unplug the cluster PC board connector

        YOU CAN JIG UP the cluster to power and use resistors to simulate the senders and check the gauges. They both read the same with same sender resistance. You can also check gauge against (accurately) measured fuel sender resistance. AKA if it reads about 1/2 tank for R, then the gauge should read "about that."

        Resistances:

        c-3826-jpg-jpg.jpg

        Possible troubles:

        Bad sender, grounding, connection, bad wire connection at the sender, broken wire in harness, bad connection at the kick panel connector

        Bad connection at the cluster PC board connector pin, bad IVR or bad IVR connecitons, bad connections at the gauge studs, or bad gauge

        There's an old thread on here about repairng/ soldering the PC board connector pins to the board traces. Also you need to solder jumpers across the board traces to the contact fingers for the IVR. The gauges---loosen /tighten the stud nuts a few times to scrub the board traces clean.

        While you are in there I'd clean/ replace the board/ lamp sockets/ lamps etc
         
        Last edited: Nov 20, 2021
      • 73 Duster 360

        73 Duster 360 Well-Known Member

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        This is helpful. Except that 'mating connector' is where the previous owner spliced a rats nest of wires to connect the after market gauge that never worked.

        So if I attach a voltmeter to the side of the mating connector that leads to the back of the vehicle pin by pin one of those should lead to the sending unit correct?
         
      • Dana67Dart

        Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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        On the back of you instrument cluster there should be cir boards. The boards have pins that connect to connectors. The back of each gauge contacts the cir board.

        This is the ammeter side of a 70 something but will give you an idea what I'm talking about.

        16374623479756371674502557608334.jpg

        You can trace out where each pin goes to

        Each gauge (except ammeter) will contact part of the cir board that goes to the IVR

        The cluster will either be directly grounded to the car body by it's mounting screws of a dedicated ground wire to the car body.

        EXCEPT for the ammeter no wires connect directly to the gauge.


        This is the fuel gauge side without the cir board the 5V mark goes to the IVR.

        The F goes to the fuel sender
        The T goes to the temp sender.

        16374628512218850656951773239123.jpg
         
      • Professor Fate

        Professor Fate Push the button, Max...

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        First, there is no "power wire from the sending unit to the dash". You're thinking backwards on this. The dash cluster is powered, with power feeding FROM each of the gauges to their individual sending units, which are nothing more than variable grounds. In the case of the fuel sender, power comes through the wire to the sender which provides variable resistance dependent on float (fuel) level. This is why, if you touch the wire to ground, it will make the gauge register full, like toolmanmike suggested. It goes to ground through the sender body/lock ring/tank, which is still insulated from body ground by the tank straps' rubber insulators and tank pad- so the circuit to ground gets completed by a clip-on ground strap that attaches to the sender barb and the fuel line, "bridging" the short section of rubber hose attached to the sender.
        th?id=OP.45MLa7pNB6zBeg474C474&o=5&pid=21.jpg
        Without this strap the sender cannot ground itself and the gauge will not function. Alternatively, a ground strap can be run from the tank pinchweld to the frame, allowing the sender to achieve ground.
         
      • 73 Duster 360

        73 Duster 360 Well-Known Member

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        Thanks for the suggestions I went ahead and ordered a ground clip for the sending unit just in case although I did ground the unit with a wire to the frame. You can never be too careful.

        While I wait for that my plan for tomorrow is to first ground the wire on the sending unit where it connects to the tank and see if the gauge moves when I turn on the key.

        If it does not my next step is to disconnect the mating connector under the left kick panel and find the pin that connects to the sending unit to see if I have a signal up to that point.

        If I do then my next step is to figure out if the corresponding wire on the top of the mating connection has been completely disconnected from the loom that leads to the instrument cluster. If it has been then I'll figure out how to rewire that up to the instrument cluster.

        If that wire hasn't been butchered and still leads up to instrument cluster but still doesn't work then I have no idea what to do next.
         
      • 67Dart273

        67Dart273 FABO Gold Member FABO Gold Member

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        If the wiring is still the original actual wire/ harness, regardless of connector, you should be able to look up "what the connector was" and get the wire color. I'll be back.........

        Start with page 8-171 of the manual, they are calling this the (CB-1) the "instrument panel and body connector"

        You can see that there is a G4 Dark BLue wire there and so that is the sender termination at the PC board.

        THERE IS NO diagram of the PC board, but you can easily follow the traces to see where they go.

        CB1.jpg

        But..........that does not tell you the wire function, so now we find the tank sender wire..........and that is "CB-9" actually on that same page

        sender.jpg

        So wire G4 and it's Dark BLue, so the connector pin is 2, but if the connector is gone, we at least know "dark blue"

        Then we go find the cluster connector. "CB" is "Connector, Body", "CI" are "Connector, Instrument", and "CE" are "Connector, Engine bay"

        cluster.jpg
         
        Last edited: Nov 20, 2021
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        • 67Dart273

          67Dart273 FABO Gold Member FABO Gold Member

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          General steps based on what you've said:

          1...Ground sender wire at tank, turn on key and see if gauge pins. If not, identify sender wire up at kick panel and ground the "forward" end of the connector and try again.

          If that causes the gauge to peg, then resistance check the wire from the kick panel to the tank. First suspect is sender grounding, second is wire end terminals..........the angled terminal at rear, and the kick panel connector (or splice) in the kick panel

          2...If test one does not cause gauge to peg, AND IF the temp gauge works (you can test it same--disconnect temp sender, ground the wire, see if temp gauge pegs---if temp gauge works and oil does not, time to pull the cluster as I outlined in the previous post

          These are really quite simple
          Power from ignition switch fees to cluster, and to IVR, which knocks down power to one stud at each gauge. the other studs go to the senders and ground

          If neither gauge works, it may be sender, or wiring/ PC board problems

          If temp works and oil does not, go through the steps in the previous post You are down to the PC board, harness pins at the connector, gauge stud connections, or the gauge
           
        • 73 Duster 360

          73 Duster 360 Well-Known Member

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          PXL_20211121_033932344.jpg
          Okay now I've narrowed it down a bit. The dark blue wire has been cut. So now I know ground or no ground I have to connect to that wire and run it up to the pin where g4 connects.
           
        • RedFish

          RedFish FABO Gold Member FABO Gold Member

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          So the dk blue sender wire has been cut at at the kick panel. I would think both ends of it are still there somewhere. Just put it back together?
           
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          • 67Dart273

            67Dart273 FABO Gold Member FABO Gold Member

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            I can't tell. Looks like the blue has been "all mashed up??"

            But yeh.........make it "continuous" again. Before you do I would (as I said earlier) test the gauge by grounding the end going up into the dash area, and see if that much "works"
             
          • 73 Duster 360

            73 Duster 360 Well-Known Member

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            So I reconnected the wire and BOOM gauge moves! Not sure if I'll have other sending unit issues as I know alot of after market parts are garbage and don't work properly but I have about 5 gallons in the tank and the gauge moved to the last line. I call that a success.

            Thank you everybody who chimed in and provided helpful insight into the problem. You guys are awesome.
             
          • 67Dart273

            67Dart273 FABO Gold Member FABO Gold Member

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            !!PROGRESS!!! "however slight" LOL
             
          • Dana67Dart

            Dana67Dart The parts you don't add don't cause you no trouble FABO Gold Member

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            Basic gauge readings


            OEM sender
            (gauge readings)
            18 gallons = full to slightly over full.
            13 1/2 gallons = 3/4 tank
            9 gallons = 1/2 tank
            4 1/2 gallons = 1/4 tank

            after market sender
            (gauge readings)
            9 to 18 gallons = full
            7 to 9 gallons = 1/2 tank
            Empty to 7 gallons = empty
             
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            • Ironracer

              Ironracer Gearhead

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              Been there, done that, more than once! My ol Harley is still that way, lol
               
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