Temp gauge problems.

Electrical and Ignition

  1. 68_Valiant_Wilson

    68_Valiant_Wilson Active Member

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    I'm having problems with my either temperature gauge, my temperature sender, or the wire running to gauge and sender. I'm really clueless as to what is wrong. I just know that my temperature gauge stays below cold constantly. How do I test it or what should I test first? My gas gauge works fine. My oil pressure light is also out. I did end up hooking up the battery backwards On accident. I'm really just clueless on where to start testing and how to test it. Again all lights, blinkers, wipers, and gauges work except for the temp gauge and the oil pressure light.
     
  2. 68_Valiant_Wilson

    68_Valiant_Wilson Active Member

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    NOTE: the car runs just fine. I'm just a little anxious about driving it without the temperature gauge and the oil light working
     
  3. 67Dart273

    67Dart273 FABO Gold Member FABO Gold Member

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    The "quickie" test for either oil or temp is to ground the sender wire and turn the key to "run." The oil light should be active, and the temp gauge should head quickly to hot. Don't leave it there for long

    I cannot remember what a 68 Val dash cluster looks like "behind." It might be there's an interconnect between two sections, etc

    Switched ignition power goes to the cluster, where it powers the IVR/ limiter. From there power goes to the fuel and temp gauge, through the gauges, and out their respective sender wires to the senders, which produce a variable resistance to ground

    You have a shop manual?
     
  4. Tooljunkie

    Tooljunkie King of cobble/master of the broken bolt FABO Gold Member

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    If everything else is normal, then suspect temp sender. As mentioned, ground sender wire to ground to test wiring. There was an overheating thread recently that mentioned a part number that is more correct than the generic sender. Also, an infra-red thermometer will be a good investment. Oil pressure could be a bulb out too.
     
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    • 68_Valiant_Wilson

      68_Valiant_Wilson Active Member

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      I do have a shop manual. Here's a pic of what the back of the instrument cluster looks like according to the book.

      image.jpg
       
    • 67Dart273

      67Dart273 FABO Gold Member FABO Gold Member

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      This may or may not be better LOL

      The IVR is your instrument regulator / limiter. The dotted trace goes to both gauges, marked "5V" is the output of the limiter. The gauge nuts are suspect because you say one of them works

      The terminals marked 'S' and 'S1' are the respective senders and go off via a board trace to the connector pins

      68val.jpg
       
    • 1968FormulaS340

      1968FormulaS340 Well-Known Member

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      Have you verified that your car isn't just running cold? A thermostat stuck open or a missing thermostat could cause a low reading.
       
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      • 68_Valiant_Wilson

        68_Valiant_Wilson Active Member

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        I thought about that too and and even if the car was just running cold the gauge sits below the cold mark and stays there no matter how much I push the car or or let it sit. The thermostat being stuck is another possibility I guess but it worked fine a few weeks earlier and I don't know why it would just up and quit working. How would I go about testing any of it?
         
      • RedFish

        RedFish Well-Known Member

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        Still the first thing to do is get a jumper wire w/ alligator clips. Jump the purple sender wire to ground then turn the switch on. If the temp gauge needle races toward the 'H', turn switch off ( this zero resistance condition for extended period can damage the gauge ) and replace the sender. Temp senders do just up and die for no apparent reason. Maybe water eventually gets to where it shouldn't? I don't know.
        The oil sender has a pizz poor wire terminal ( slides horizontal over a little round button contact ) and on a LA is down below behind the distributor. Its not uncommon for that terminal to get bumped off the sender. Short that gray wire to ground, light should come on with switch on if the bulb is good.
         
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        • 67Dart273

          67Dart273 FABO Gold Member FABO Gold Member

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          ^^Yup^^ Already told him that. OP, what HAVE you done?

          I forgot to mention that one "popular" problem is the nuts get loose/ corroded on the gauge studs
           
        • Dartswinger70

          Dartswinger70 Catch a wave youll be sittin on top of the world

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          You don't need a temp gauge, just run it till you see steam and smell anti freeze... you'll hear it pinging also. [​IMG] :D
           
        • 68_Valiant_Wilson

          68_Valiant_Wilson Active Member

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          I haven't really been able to do any testing due to the rain I've been having the past several days and the fact I don't have a garage. I'll test it asap.
           
        • 68_Valiant_Wilson

          68_Valiant_Wilson Active Member

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          Thanks for that advice man. That was exactly what happened to my oil light. Took me awhile to figure out where my oil pressure switch was but I got it working thanks.
           
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