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1995 Ranger-Does Temp Gauge have resistor

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Old 06-14-2018
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1995 Ranger-Does Temp Gauge have resistor

I have a 1995 Ford ranger XLT 3.0. Dead temp gauge. Got a replacement from junk yard. Exact same numbers. But the new one does not have a resistor like the old one. And it pegs to hot. Do I need to transfer the resistor? Taken from a junked Ranger instrument cluster.
 
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Old 06-14-2018
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Didn't think it did, resistor is the Sender

But will not hurt anything to transfer it over, for sure
So try it
 
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Old 06-14-2018
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Down the Rabbit Hole

Strange. The resistor is not shown on any temp gauges on sale at eBay. But it is made to slip on the temp gauge pegs. Looks factory. I swapped it on the new gauge that pegs hot and no change. So why did someone put on a 92 ohm resistor? And I wonder if it helped fry the old gauge; even though a resistor should not do that. You can easily slip off the old resistor and onto the new pegs. Not homemade. Totally strange.
 
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Old 06-14-2018
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I did not one number difference in the two clusters. Maybe Ford later deleted the resistor or added it. Any Ford experts know the story?
 
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Old 06-14-2018
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Ford did have resistor on Oil Pressure gauge, when they changed to a switch on the engine.
Although that was on circuit board.

You would use a resistor like that to set a Maximum resistance, of 92ohms, so when you turn on the key gauge needle would move to COLD, unless sender was lower resistance then needle would go up to that resistance.
i.e. 0 ohms is no resistance, like when you ground the wire at the sender and needle goes to HOT.
So 92 ohm resistor set needle range from 92 ohms to 0 ohms

Older Ford temp senders were 75 ohms COLD, 10 ohms HOT, can't say if newer ones are different ohms, but ohms should go down as temp goes up

This is OPPOSITE of temp SENSORS, ECT sensor gets HIGHER resistance(lower voltage) as temp goes up
 
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Old 06-15-2018
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30 OHM cold?

Unless I am doing it wrong, I get 30ohm from temp sensor cold. I believe this is correct. So why would the gauge peg to hot? Resistor has no effect. Thinking of trying a higher value resistor.
 
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Old 06-15-2018
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Ford temp gauge can have internal 100 ohms resistor or external 100 ohm, 92 is close enough

Resistors hooked up that way is called a Parallel resistor circuit, which is much different than when you hook resistors up in series, which just adds resistance, i.e. 100 ohms + 100 ohms = 200 ohms total resistance in series

In Parallel you need to divide resistance
Parallel resistance calculator here: Parallel Resistor Calculator R1 + R2 = equivalent resistor R resistance circuit equiv total resistor finder made easy piggyback = parallel - sengpielaudio Sengpiel Berlin

Easier to use a calculator than to do math yourself, but formula is there

If you have 92ohm(gauge) and then sender is 30 ohm cold, you get 22 ohm which would be close to HOT, 10ohms

If sender was 75ohm and gauge was 92ohm then you get 43ohm at the needle for COLD, and 9ohms for HOT

So looking at that, 22ohm should be about 1/2 on gauge, not HOT, it is not linear, its a curve, but near 1/2 should be accurate
 

Last edited by RonD; 06-15-2018 at 11:29 AM.
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Old 06-15-2018
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Back to the Future

Since the original issue was a dead temp gauge, I am going to reinstall the original sending unit and see what happens. Perhaps the new one I installed is faulty.
 
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Old 06-15-2018
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Its a pretty simple circuit

Instrument cluster(12volt)------gauge-------(wire to engine bay)------------sender---ground(threads on sender)
 
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