Bench test rallye gauges

1971 - 1974 Mopars

  1. USatC

    USatC Well-Known Member

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    Okay guys I pulled my gauge cluster and now i’m a little lost for how to troubleshoot. In my Chrysler manual, they make note of a testing unit that I do not have. My question is does anyone know of an effective way to test the gauges in my 72 Rallye cluster.
     
  2. PurpleBeeper

    PurpleBeeper Well-Known Member

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    One critical thing I believe it NOT to run 12V directly to the gauges. There is a voltage limiter in the dash circuit (often goes out) that drops the voltage down to 5V (or 7V, can't remember). If that limiter is good, then run 12V through the limiter & ground the other end of each gauges circuit.

    I vaguely recall seeing something (on youtube) about somebody stacking together regular household batteries to use as a power source to test temp/fuel/oil, so maybe check that too. I really have no idea how to test an amp meter.
     
  3. 451Mopar

    451Mopar Well-Known Member

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    I have some old notes when I checked my 1969 rally gauges with the 5 volt linear (7805 type regulator):
    Oil Pressure:
    0 PSI, 74-82 mA, around 51 to 43 Ohms.
    15 PSI, 108 mA, 30 Ohms.
    20 PSI, 113 mA, 28 Ohms (2, 56 Ohm resistors in parallel.)
    40 PSI, 136 mA, 20 Ohms
    60 PSI, 156 mA, 16 Ohms
    80 PSI, 172 mA, 9.79 Ohms (10 Ohm in parallel with a 470 Ohm resistor.)

    Fuel Gauge:
    Empty, 51 Ohms
    1/4 Tank, 50 mA, 33 Ohm
    1/2 Tank, 100 mA, 20 Ohm
    3/4 Tank, 125 mA, 15 Ohm
    Full, 150 mA, 10 Ohm

    Temp Gauge:
    120 Degrees, 62.1 mA, 62 Ohms
    150 Degrees, 98.8 mA, 33 Ohms
    170 Degrees, 119.7 mA, 22 Ohms
    180 Degrees, 130 mA, 20 Ohms
    225-230 Degrees, 160 mA, 13 Ohms
    240 Degrees, 163 mA, 12 Ohms
     
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    • Nacho-RT74

      Nacho-RT74 FBBO Gold Member FBBO Gold Member

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      just to check if they work, a 9 volts batt will work, or even 2 AA batts in series to get 3 volts... if using a 9 volts batt for a second to watch the needle moving, because as mentioned, they work with 5 volts.

      to calibrate, thats another stuff
       
    • USatC

      USatC Well-Known Member

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      Just run the pos and neg from the batter to the two post?
       
    • Daves69

      Daves69 Well-Known Member

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    • Nacho-RT74

      Nacho-RT74 FBBO Gold Member FBBO Gold Member

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      Yes.

      You can make it also with an old phone wall charger. The old ones ( not USB ) uses to be 3.7volts or so.

      Or if you have an USB with ends easy to attach to the gauge posts

      Or any other power source on that DC rate. But if some source is above 5 volts, keep an eye on gauges, because you could get burnt gauges ( the 9 volts batt test needs attention ). Barely feed them enough to watch the needle move. Will move fast
       
      Last edited: Jan 6, 2019
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      • Nacho-RT74

        Nacho-RT74 FBBO Gold Member FBBO Gold Member

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        you can also test the voltage limiter at the time. Feed it with 12 volts to check if the output gets a pulsating signal... no matter the speeds of the pulse but just getting pulsating signal. That will test good. If no signal or even worst, steady 12 volts, will mean is damaged.

        Voltage limiter pulse speeds change between limiters, some are faster and short time pulse some others are slower and longer pulse. That's calibrated with speciall tools ( osciloscope I think ). The 5 volts is an RMS ( average ) measurement within pulses
         
        Last edited: Jan 6, 2019
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