1969 Plymouth gas and temp gauge not working, but voltage ok

Electrical & Ignition

  1. General23cmp

    General23cmp Well-Known Member

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    Neither gauge works. With a volt meter I checked the voltage going to my temp sender, and it appears to be pulsing voltage. While it’s a digital meter and you cannot see the exact waveform of the limiter, the numbers I see bouncing back on the meter seem like what I’d expect. Thoughts on other possible issues?
     
    Last edited: May 17, 2019
  2. BeepBeepRR

    BeepBeepRR Well-Known Member

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    Probably a bad voltage limiter. It powers both of what you are having issues with.
     
  3. General23cmp

    General23cmp Well-Known Member

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    That’s what I’m saying, it appears to be “limiting” like what I’d expect. I can clearly see it bouncing from 0V to full voltage (I think it’s supposed to do that).
     
  4. BLK 68 R/T

    BLK 68 R/T Well-Known Member

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    0 to 5 volts, if it's pushing out 12v you will fry the gauges. Try grounding the temp sensor wire for a few seconds, see if the gauge moves. Amp gauge is separate from the others so it wont be affected at all by the limiter.
     
  5. danf_fl

    danf_fl Well-Known Member

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    What is resistance at fuel sender unit? It should be steady.
     
  6. General23cmp

    General23cmp Well-Known Member

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    Amp gauge works. I’m pulsing between 0 and 5. I have tried grounding and had no movement.

    Brand new fuel sender. It’s good. I have it temporarily connected to an aftermarket gauge so I know fuel level.
     
  7. Sixpactogo

    Sixpactogo Well-Known Member

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    Check the connectors that slide onto the pins on the printed circuit board. I had a couple connectors on my 68 harness that were opened up a little and not making a good connection on the pins. Both the gas gauge and temp gauge were not reading properly until I squeezed those connectors a little tighter and sprayed some electrical connection spray on them. Work fine now. Sometimes it's the little things like that has us pulling our hair out trying to figure out what is going on. If the senders are doing what they should and limiter is working the usual problem is bad connections or bad grounds. Make sure your cluster is grounded since that is where the gauges get their reference to ground. If you painted your dash frame like I did, chances are that is your problem.
     
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    • General23cmp

      General23cmp Well-Known Member

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      Thanks. That sounds like a good next step. I was hoping to avoid pulling it all out, but I’ll do what I need to do.

      I assume if the limiter is putting out voltage, all fuses are likely good.

      Do they remake the fuel and temp gauges if these are fried?
       
    • Sixpactogo

      Sixpactogo Well-Known Member

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      You may find some NOS ones from time to time on Ebay but if it were me, I would send them to Shannon Hudson at Redline Gaugeworks and have them rebuilt. They would come back calibrated and ready to tell the truth. I sent my whole cluster to them for restoration. I had them replace the Amp meter with a volt meter and rebuild and reface the other three. There are others out there that do a good job too.
       
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      • General23cmp

        General23cmp Well-Known Member

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        Thanks. I may pull the whole thing and do that.

        It does seem odd that the two that run off that limiter are the two not working, but my meter is showing what appears to be a good pulse.

        I also just tried putting an old dash bulb between the temp sender and the firewall, and it lightly pulsed as you’d expect.
         
        Last edited: May 18, 2019
      • General23cmp

        General23cmp Well-Known Member

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        So, can someone explain the circuit to me? Let’s just talk temp gauge as my fuel isn’t even connected at the moment. Is it not just a pulsing 5v signal passing thru the gauge and to the sender? In other words, no reference? I thought it’s simply the 5v pulsing, and the varying resistance of the sender causes varying “heat” thru a coil in the gauge to turn the needle. One connection in the gauge and one out, right? So, if I’m seeing a pulse at the sender, that should be passing through the gauge, right... Thus, I have the circuit (not a bad connection) and my gauge is just bad?
         
      • mopar 3 B

        mopar 3 B Well-Known Member

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        Who said anything about the amp gauge. A 12 volt test lamp plugged into the disconnected temp sensor wire will indicate a working limiter if it is flashing. If not its bad. Also to the OP are the gas and temp gauges not moving at all or pegged to their max? The first could be a bad board and the later a bad ground.
         
      • General23cmp

        General23cmp Well-Known Member

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        Thanks. The gauges aren’t budging off 0. What do you mean “bad board”? Would a bad board not also result in a test light not flashing? I get flashing at the temp sender wire.
         
      • mopar 3 B

        mopar 3 B Well-Known Member

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        Correct voltage must travel threw the board to get a flash at the temp sender wire. Don't write the gauge off until you know the sender is good. If the gauge is good a momentary grounding of the sender wire should bring the gauge off 0. Do not allow the gauge to reach its high limit or damage can occur. This should only take a few seconds.
         
      • General23cmp

        General23cmp Well-Known Member

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        Grounding my pulsing sender wire doesn’t move the gauge.
         
      • mopar 3 B

        mopar 3 B Well-Known Member

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        So
        Sounds like gauge recondition or replacement time. If so inclined it maybe time to just send the whole cluster out for a rebuild. I have no one to recommend as I am still going threw a pile of stashed parts (not for sale).
         
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