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Gauge Tags/Tach Testing  Rating:  Rating
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 Posted: 02-15-2006 07:45 pm
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Jim DeClerck
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  I have the instrument panel out of 19336 for cleaning and noticed that each instrument has a small numbered white paper tag glued to its back.  Most are unique but the Volts and Temp gauge tags have the same number.  The numbers are: Volts - 444, Oil - 484, Speedometer - 414, Tachometer - 482, Temp - 444, Fuel - 454.

  Also my PO included with the car 2 additional JH tachometers with tags 164 and 424.  These numbers do not match nor do they match one installed in the panel.  Curiosity compels me to ask if anyone knows the significance of the numbered tags. 

  BTW there is also a larger paper tag tied the the panel wiring harness with  three numbers on it: 54960862D, a handwritten and circled 2205, and a small stamped 32 partially enclosed by a "U". Same question.

  Finally, is there a multimeter way, without installing a tachometer and running the car, to test whether it is operating condition?  Visually everything seems to be in order with all the tachs and I'm ready to reinstall the panel with  482 but I'd prefer not to have to remove and reinstall the panel again if the one in the panel now doesn't work.  It wasn't connected (no wonder it didn't work) when I bought the car so I'm not sure it or the others are good to go.

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 Posted: 02-16-2006 05:54 am
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Mark Rosenbaum
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Very probably the number stickers on the backs of the gauges refer to either the person who assembled the gauge, or, more likely, the one who inspected it to make sure it worked correctly.  I don't know of any other significance to them.

For the panel wiring harness, 54960862D is the Lucas drawing number.  The Jensen part number would have been 90843.  Not certain what the 2205 is, perhaps it's a date code of some sort.  The 32 in a U sounds like an inspector's approval stamp.

To test the tach without the engine running, you'd have to provide power for the tach and switch a 4-amp current on and off at the same rate as the points would switch the coil current.  For example, 3600 rpm is 60 revs/second, which, since the engine is a 4-cylinder 4-stroke design, means 120 current pulses per second.  You could do this with some fairly simple electronic circuitry, or you could dismount the distributor and spin its shaft at a known speed with the wiring hooked up normally and the ignition switch in the ON position.

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 Posted: 02-17-2006 08:21 am
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Jim DeClerck
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Thanks, Mark.  All I have is a multimeter, so I'll reinstall the gauges and start the engine to verify operation of the tach.  Later I can see if it needs to be calibrated.  Your assistance is appreciated.

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 Posted: 02-18-2006 11:56 pm
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Jim DeClerck
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  Trouble.  I installed the instrument panel in the car and ran it but the tach is not responding.  verything else works.  I have 2 spare tachs from the PO and would like to check them while running the engine, but before I tear out the instrument panel again, can I connect the a ground to one of the tach retaining screws and 2 - 3 of the other plugs to components under the hood with clips on wires and expect a tach to operate?  There are 3 wires, white w/gray stripe, white and green connected to plugs in the back of the tach.  Where do these connect under the hood?  I tried to trace them on the wiring diagram but haven't had much luck.  The car is equipped with a Pertronics unit in the distributor.

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 Posted: 02-19-2006 12:17 am
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Mark Rosenbaum
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"... can I connect the a ground to one of the tach retaining screws and 2 - 3 of the other plugs to components under the hood with clips on wires and expect a tach to operate?"

Yes, you can test a tach that way.

The green wire is the power supply for the tach.  This should be +12 volts when the ignition switch is ON.  The black wire connects to the body of the tach, and goes to chassis ground.

My wiring diagram claims that the two remaining wires are both white but in many cars one of them is white-grey (AKA white-slate).  In any event, one of these wires comes from the ignition switch and should read +12 volts when the switch is ON.  The other wire goes to the ballast resistor in the engine bay.  The far side of the ballast resistor goes to the + side of the coil, and to the terminal on the starter solenoid that bypasses the ballast during cranking (only).

I don't know whether the male pin on the tach goes to the +12 volts or to the ballast, you'd have to check your wiring harness.

 

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 Posted: 02-19-2006 04:47 pm
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Jim DeClerck
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  Maybe it doesn't matter which of the 2 white (according to the wiring diagram you and I both have) wires.  The all white wire has a female bullet connector which plugs into the male bullet terminal on the tach.  The white-slate wire has a male bullet connector which plugs into the female terminal on the tach.  Does that help?  I don't want to damage a tach by connecting the white and the white-slate wires to the wrong current sources.  Since the terminals are opposite it appears someone thought they should be connected only one way.

  This car has had the 2.2 ltr modification, has Pertronics ignition and appears to have no ballast resistor.

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 Posted: 02-19-2006 06:58 pm
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Mark Rosenbaum
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It probably does matter which way the two white wires go.  While it seems unlikely that you could damage a tach by reversing the connections, it probably wouldn't work right, or might read incorrectly.

With that in mind, I just took a glance at the wiring on my car.  On it, the white-slate wire goes to the ballast resistor.  Therefore, the male pin on your tach should connect to a high-current (about 8 amps peak) +12 volt supply, and the female pin on your tach should connect to the ballast or coil {+} terminal.  This should replicate the way the factory plug is connected.

Bear in mind that some JHs and/or GTs used a ballast wire instead of a ballast resistor.  I've never actually seen a car with this arrangement, and consequently don't know how they handled the ballast bypass wiring from the starter.  Possibly they would have just left it unconnected.

You should also be aware that some owners have reported that their tachs don't work after they install a Pertronix device.  AFAIK no one has ever taken a close look at this, so it's uncertain why it occurs, but perhaps the tachs in question were marginal, or it may be related to the coil used.  I would not think it at all likely that the Pertronix gadget itself was the culprit.

 

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 Posted: 02-19-2006 10:36 pm
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Jim DeClerck
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Thanks, Mark.  Now I'll have more confidence when I go under the hood to diagnose the fault I'm experiencing.  Back to the garage....

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 Posted: 04-24-2006 12:34 pm
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cjwilson
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Hey Mark-

My 73 JH had the Pertronix unit installed when I purchased it. It also had a non-functional tach, and no ballast resistor. 

I fried the Pertronix unit in a moment of stupidity about 2 years ago. Funds being what they were at the time, I decided to go back to points and condenser. Car has been working fine ever since.

I am now working my way through the dash, as my tach, fuel and temp gauges have never worked since I bought the car. I'll post more as I make progress.

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 Posted: 04-24-2006 03:36 pm
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Mark Rosenbaum
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CJ-
I can't add anything that might help with your tach, but the fuel and temp gauges get their power from the voltage stabilizer, which is a small metal box located above and behind them on the interior side of the instrument pod.  This operates something like a turn signal flasher and applies 12 volts  to the two gauges for a while, then zero volts for a while, etc., giving an average of about 10 volts.  If it's dead, those two gauges won't work.

 

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 Posted: 04-24-2006 11:03 pm
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John Finch
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18309's voltage stabilizer died last fall and I lost the fuel and temp guages. I replaced it with the ss one advertised on ebay. Works great so far. John

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 Posted: 04-28-2006 01:23 pm
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cjwilson
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I pulled the voltage stabilizer apart and cleaned and reconnected it. Now my temp gauge works but fuel gauge doesn't. I pulled the fuel tank sending unit and when I tested it with an ohmmeter, I found that the windings were broken. I then drilled out the two rivets and found the broken winding on the reverse side. I tried to solder the windings and it worked, but I'm not confident for how long and I know the gauge isn't completely accurate now, but it's better than it's ever been.

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