# Gauge problem 66 GTO



## Richie Cat (Aug 4, 2008)

I have issues with my gauges. First off my gas, temp and oil pressure are incorrect. My tach don't work but that's another story. I have checked all grounds and they prove positive. Am I looking at voltage drop to them?


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## 05GTO (Oct 6, 2004)

Where does your negative battery cable connect on the car?


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## Richie Cat (Aug 4, 2008)

Negitive battery cable is to engine. Extra pigtail off cable goes to radiator support. Have braded ground wire from engine to firewall. I have run a complete seperate ground wire from gauge cluster to bat. neg. With no effect.


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## Richie Cat (Aug 4, 2008)

Also have to say, water and oil pressure do go their full range with the sending wire open or shorted to ground. The gas guage reads 3/4 full with the key on or not. I have 15 gal. in tank. Thanks again for the help with the horn button. It works fine now.


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## Eric Animal (Oct 28, 2007)

Corroded or bad senders.....


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## Richie Cat (Aug 4, 2008)

Their brand new senders. Never measured resistance of sender wire to gauge though. Thanks for the input.


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## Rukee (Feb 8, 2007)

If you can make the gauges work right by removing and grounding the sensor wires then the sending units must not be the right ones or calibrated for your gauges.
Maybe you have the ralley gauges and sending units for gauges with idiot lights? IDK.


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## Richie Cat (Aug 4, 2008)

I told the local parts house to send me senders for gauges. They had them in stock. The name of the company is Standard. When first starting engine, cold temp gauge is at bottom of scale, as it warms up it will show maybe 220. With a temp. gun I see 170 at the crossover passage water pump to intake manifold. Oil pressure with key on is zero, engine running it is pegged past 60 psi. I used a mechanical oil pressure gauge and when at operating temp,by heat gun, oil pressure is 50 psi at idle but oil gauge still reads over 60.


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## Rukee (Feb 8, 2007)

Doesn`t sound like it`s too far off. Remember on the cooling system your temp gun is showing the outside surface temp of the intake manifold, not the actual coolant temp which may be slightly higher, but not the 220 you see on the gauge. I have one of those temp guns too, it`s a great tool to have! And as long as the oil pressure goes to zero when it has no pressure, then the rest doesn`t matter, as long as you know it has pressure that`s the main thing. It kinda sounds like they have a unit for a light and not a gauge for the oil. It should be a bell style sending unit.
My car just has the idiot lights so I don`t see any change sept for they come on before I start the car.
Try a temp sending unit from another parts store, like NAPA or something and see if it`s closer.


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## geeteeohguy (Feb 2, 2008)

Sounds normal to me. The rally guages tend to be a bit optimistic: The tachometers and guages tend to read a little high. I've had three '66 GTO's and still have a '65 with the rally guages, and ALL of them read 60psi on fire-up. Don't worry about it. As for the fuel, it will read what the level was in thetank when it was shut off. If you have 15 gallons, thats about exactly 3/4 tank of fuel: you have about a 20 gallon tank. The guage shold peg to full when you disconnect the wire at the tank if the guage is working. No Rocket science involved here, just make sure the grounds are clean, the voltage drops are not excessive, and that the resistance levels are ok (directly related to the voltage drop!) . If you're worried that your oil guage and temp guages are slightly off, (normal), perhaps you can send the cluster out and have new, high tech (accurate) guages installed. Good luck!
Jeff


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## Richie Cat (Aug 4, 2008)

Rukee, I still have a bell style sender for the oil pressure vs. one that looks like one for light. Both do the same thing. How could these gauges be so insensitive to the actual readings? I really don't think back in 66 when they made the car, these gauge were meant to be off calibrated. And no, I'm not buying hi tech gauges to get around this problem.


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## Richie Cat (Aug 4, 2008)

Back one more time before I go out. Geeteeoguy, you talk about voltage drop. How much is too much? And if the senders I do have are not calibrated correctly to the gauges do you think getting them from Ames is a better choice?


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## geeteeohguy (Feb 2, 2008)

Richie Cat: The basic rule of thumb is no more than .1 volts voltage drop (a tenth of a volt). You can look all this stuff up on line, if you need to. As for the sending units, I don't know that Ames's would be any better, though my experience with Ames has always been excellent. What you could do is calibrate your existing guage with an in-line resistor.....just hook up a mechanical guage inline, and increse the resistance of the circuit until the readings match. You can do this with a rheostat (adjustable resistor), find what setting is the correct one (by checking with an ohmmeter when the readings match), and soldering in an in-line resistor (from Radio Shack, etc.). Nobody would see it (they're tiny), and you would have accurate and original guages.


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## Rukee (Feb 8, 2007)

That would work if he needed the gauge to read more temp then it does now, but he wants it to read less temp, which would mean he needs to decrease the resistance, not add to it. 
Like I said, as long as the gauges are working, I would just note, or make a mark on the face of the temp gauge at the point of normal temp. You could even pull the sending unit out and in a bucket of water, grounded to the car, heated with an external source, temp cross checked with your thermal gun, you could calibrate were overheating would be and mark the face there as well. Or try a different brand sending unit.


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## Richie Cat (Aug 4, 2008)

Back from my day trip.Thanks gentleman for your knowledge and ideas I'm going to check resistance to guages and try another brand of sending units. Would like to see if I can get ac/delco parts.


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## geeteeohguy (Feb 2, 2008)

Good points, Rukee. He could try a thermistor type sensor, where the resistance decreases as temperature increases, like some coolant temp sensors do. I think he'll get it figured out.
Jeff


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## Richie Cat (Aug 4, 2008)

Just an update for everyone. I found a company called California Pontiac Restoration Parts. From what their email said to me, they have the correct temp. sender for rally gauges (p/n 6402383,$16.50) Also Ames has a oil pressure sender (p/n M195,$29.00) that is also correct. Could not find ac/ delco parts. Wires to gauges are fine. Going back to basics and start at the begining. When parts are installed, I'll let you know what happened.


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