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I bought a reproduction temp gauge from Ricks a couple of years ago,for my 68 Camaro(the factory gauge setup), and it read all the way over on HOT as soon as I started the engine. I was looking at an older catalog recently, and discovered a note that said not to use the resistor on the back of the factory gauge. Upon reading this, I tore apart my gauges again, and I see two pieces mounted to the back of the gauge. One looks like a ceramic type piece, kind of thick and heavier than the other piece, which is much smaller and thinner. Which piece, or is it BOTH pieces that have to be removed to make it work properly? Thanks in advance for any help in this matter, as I am clueless when it comes to electrical issues.
 

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He's wrong unless they have totally redesigned the gauge and built the resistor into the inside of the gauge. You need the resistor to make the gauge work. The resistor drives the gauge downscale (towards "C") otherwise the gauge will rise very quickly to the H peg as soon as you turn the car on, and it will stay there forever. The resistor provides counter EMF to balance the guage and drive it back downscale as the car cools. The resistor is an 84 ohm unit. Check it to make sure you have the right one. This resistor makes the gauge read just about 1 or 2 lines above the 1/4 scale mark when it's hot. If you replace it witha 91 ohm resistor it will make the guage read right below the center mark on the gauge.

The other thicker peice of plastic is an insulator that keeps you from shorting the terminals out to the back of the gauge mounting plate.

See the attached picture, the temperature gauge is the front right gauge in the picture.

http://home.townisp.com/~markcanning/camaro/gauge1.jpg
 

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Thanks for the reply and the pics Mark. I had the setup the same as your pic. I phoned Ricks for some tech questions yesterday. They explained that I did need to leave the resistor off to get an accurate reading. I removed the resistor as they suggested, and I get no reading at all. I really hate to hook the aftermarket temp gauge back up, I would like to have all of the factory gauges working properly. Mark, if you or anyone has experienced similar problems or can help resolve this issue, any help would be appreciated.
 

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I guess I should have also mentioned that you have to ground the rear mounting plate in order to get the gauge to work right. There is a ground wire in the harness but most people hook it to the front (fuel and oil pressure)mounting plate run a jumper from the front plate to the rear plate if you have the gauges wired this way. The lower terminal on the resistor is the ground connection for the temperature gauge, the upper should be internally connected to the +12V battery lead, and it is insulated from the backing plate with a rubber grommet. Sometime both the upper an lower terminals have these grommet and in this case you need to put the ground jumper right onto the lower terminal to get it to work.

Power comes in through one of the two stab on terminals and goes out to the temperature sender through the other terminal. This is one side of the gauge operating circuit. The other side is through a set of windings inside the gauge connected to the +12V terminal inside the gauge, then through the resistor and out to ground. This second circuit allows for a fixed amount of current to flow through the gauge in a direction opposite the first circuit, that generates a fixed amount of electromagnetic force (EMF). As the temperature sender changes resistance it allows more (hotter) or less (colder) current to flow through the gauge. When there is more EMF generated in the sender circuit than the resistor circuit the gauge moves up scale towards hot. When there is less current in the sender circuit the EMF in the resistor circuit pushes the needle down scale towards cold.

That's why you need a resistor in the second circuit, so that you can balance the gauge properly. Maybe they moved the resistor inside the gauge, but I think you still need it.

Check your ground connection to the gauge, and/or the rear mounting plate.
 
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