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Which wire goes to to the temp sending unit?  Rate Topic 
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 Posted: 04-20-2007 02:06 am
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smcmanus
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I found the reason my temp guage doesn't work; there is no wire connected to the sending unit.  I then found a bundle of 2 whitish wires coming out of the harness close to the firewall that aren't connected to anything.  I tried hooking each of them to the sending unit, but still no temp reading.  There is also a black wire under the manifold that isn't hooked to anything, which I didn't try yet.  I'm not sure it will reach the sending unit.  So does anyone know which wire goes to what?  I looked but didn't find an answer in the service manual.

Thanks

Steve

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 Posted: 04-20-2007 03:27 am
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Jensen Healey
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It's supposed to be green with blue tracer.  Mine's orange.

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 Posted: 04-20-2007 03:34 am
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Mark Rosenbaum
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The temp sensor wire runs from the terminal on the sensor to the 5-pin connector set in the engine bay.  The engine end of this connector set is wired as follows:

Pin 5: green-blue, to temp sensor terminal.
Pin 4: white-red, to starter solenoid.
Pin 3: brown-yellow, to alternator.
Pin 2: white-slate, to single-wire end of ballast resistor.
Pin 1: not used.

The black wire under the manifold might be the temp sensor wire, a disused wire running to the ignition points, or something else entirely -- no way to tell without tracing it out.

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 Posted: 04-21-2007 11:57 pm
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smcmanus
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I have zero continuity from the terminal to ground so I guess the sending unit is shot.

Thanks

Steve

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 Posted: 05-01-2007 07:56 pm
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flatlanderep
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in regards to the temp sending unit and the gauge........

Would it be the wire, the gauge or the temp sending unit itself that causes inaccuracy.
It seems that during any driving condition my temp reading will get close to red. Now, its not overheating and we have checked the actual coolant temp multiple times getting readings under 160^. So I'm fairly certain its not a coolant issue as it is a gauge or sensor issue.

I just want the gauge to be accurate so in the event that it does overheat, I'll know! :)

Temp sending unit easily replacable?

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 Posted: 05-02-2007 06:21 am
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Mark Rosenbaum
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If the measured coolant temperature is circa 160° the gauge should read a needle's width (roughly) below mid-range.  If it does not, the first thing to check would be the voltage stabilizer module mounted to the forward face of the instrument pod near the fuel and temp gauges.  Normally the stabilizer produces a pulsed output that over time averages to about 10 volts; there is also a solid state version that produces a constant 10 volt output.  When a failure occurs, the stabilizer may produce a constant 12 volts, which would result in a high reading on the temp gauge and on the fuel gauge.

The temp gauge or temp sensor could be defective, but a failure in either tends to result in a dead gauge rather than an inaccurate one. Similarly, if the wiring is defective, the gauge quits operating.  Note that a previous owner might have adjusted the fuel level sender to mask the inaccuracy of the fuel gauge due to a faulty voltage stabilizer.  Further, while it is possible that a PO might have mis-calibrated the car's temp gauge, that requires a level of foolishness very rarely seen.

Drain the engine coolant before removing a temp sensor.  For installation, the case of the sensor must connect to the metal of the engine block, so one should use a sealant such as Permatex or Hylomar rather than plumber's tape.

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 Posted: 05-02-2007 03:09 pm
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flatlanderep
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Mark Rosenbaum wrote: If the measured coolant temperature is circa 160° the gauge should read a needle's width (roughly) below mid-range.  If it does not, the first thing to check would be the voltage stabilizer module mounted to the forward face of the instrument pod near the fuel and temp gauges.  Normally the stabilizer produces a pulsed output that over time averages to about 10 volts; there is also a solid state version that produces a constant 10 volt output.  When a failure occurs, the stabilizer may produce a constant 12 volts, which would result in a high reading on the temp gauge and on the fuel gauge.

The temp gauge or temp sensor could be defective, but a failure in either tends to result in a dead gauge rather than an inaccurate one. Similarly, if the wiring is defective, the gauge quits operating.  Note that a previous owner might have adjusted the fuel level sender to mask the inaccuracy of the fuel gauge due to a faulty voltage stabilizer.  Further, while it is possible that a PO might have mis-calibrated the car's temp gauge, that requires a level of foolishness very rarely seen.

Drain the engine coolant before removing a temp sensor.  For installation, the case of the sensor must connect to the metal of the engine block, so one should use a sealant such as Permatex or Hylomar rather than plumber's tape.

Thanks Mark. I was suspecting the voltage stabilizer myself.
But, I noticed the other day that the copper (?) wire that runs from the engine to the instrument panel was uncovered. Not sure if this has to do with the temp gauge. But I insulated it and now the gauge is showing right at the half way mark - where it needs to be. It could very well be a fluke but I like to think I solved the problem.

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 Posted: 05-02-2007 10:48 pm
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Mark Rosenbaum
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Well, yes, if the bare wire is shorting to the engine block, then the gauge will read high.  The way I read your question, though, it seemed to me that you were thinking the wire was some sort of resistance wire, which is not the case.

In any event, if the problem doesn't recur, it'll be fairly clear that you've fixed it.

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