78 Temp. Guage Problems
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Intermediate
Joined: Aug 2006
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78 Temp. Guage Problems
Ijust installed a new temp. guage on my 78. The instrument cluster sat on the bench for about a month waiting for the new guage to come. I forgot to take pictures of the back of the guage cluster and I can't remember how the guage was hooked up. There is a small piece of white plastic or maybe it's porcelon. Does it go horizontally or vertically accross the back of the guage. I can't find a picture in any of my manuals. Thanks Bob
Burning Brakes
Joined: Jan 2006
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From: Same as our leaders Out of my mind
The "porcelain" is a resistor, it matches the resistance of the gauge to the temperature sending unit. It mounts horizontally between the 3:00 and 9:00 terminals on the gauge. If you installed a new temperature sending unit or a new gauge you may have to change the value of the resistor to make the gauge read accurately.
I struggled with my gauges and sending units for a long time thinking I had bad gauges/units, it turns out that they were mis-matched. I ended up substituting resistors from another used gauge cluster. The resistor that worked best for me was 5 ohms lower in value. I checked the temps with an infra-red temp. gun to verify the accuracy of the gauge. It was trial and error, but persistence paid off. Good luck with your gauge.
I can help you revive your stock in dash clock too if you have one.
I struggled with my gauges and sending units for a long time thinking I had bad gauges/units, it turns out that they were mis-matched. I ended up substituting resistors from another used gauge cluster. The resistor that worked best for me was 5 ohms lower in value. I checked the temps with an infra-red temp. gun to verify the accuracy of the gauge. It was trial and error, but persistence paid off. Good luck with your gauge.
I can help you revive your stock in dash clock too if you have one.
Burning Brakes
Joined: Jan 2006
Posts: 876
Likes: 1
From: Same as our leaders Out of my mind
PICTURES - worth a thousand words
This is a late model C-3 (plastic housing) gauge cluster. I have pulled back the mylar printed circuit to expose the resistor. Note that there is a color code on the resistor. You may want to substitute a resistor of a higher or lower value depending on your results.
This is an early model C-3 (metal housing) gauge cluster. The resistors are mostly vertical.
Here you can see the other resistor color codes through the mylar on the other gauges (plastic housing).
One other very important item of interest. DO NOT SUBSTITUTE THE LITTLE STAMPED STEEL NUTS on the mylar circuit board. These stamped nuts have a specific resistance, or level of conductivity. Substituting new hardware may change the resistance values and throw off your gauge readings (ask me how I know...).
I hope this helps!
This is an early model C-3 (metal housing) gauge cluster. The resistors are mostly vertical.
Here you can see the other resistor color codes through the mylar on the other gauges (plastic housing).
One other very important item of interest. DO NOT SUBSTITUTE THE LITTLE STAMPED STEEL NUTS on the mylar circuit board. These stamped nuts have a specific resistance, or level of conductivity. Substituting new hardware may change the resistance values and throw off your gauge readings (ask me how I know...).
I hope this helps!
Burning Brakes
Joined: Jul 2005
Posts: 875
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From: California
I had the same problem on my 72 big block, purchased a correct sending unit from Electric Limited www.lectriclimited.com and problem resloved.
Le Mans Master
Joined: Jan 2006
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From: GA "When I grow up, I'm gonna get a Trans Am and run from the cops". Direct quote from my 4yo son.
Bob, was your gauge reading all over the place or sort of not reading at all? I know my temp gauge has power, but the temp never really comes up. I replaced the sending unit with an auto parts store one with no change. I'm curious as to where others stand in relation to my problem before I start chasing gremlins.
Burning Brakes
Joined: Jan 2006
Posts: 876
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From: Same as our leaders Out of my mind
Originally Posted by Rclarendon
Thanks for everyones help. I checked the blue labeled resistor on back of temp gauge with a Ohm meter and no continuity. Where do I get a new one. Thanks Bob.
I bought a used panel off of the 'net for parts. I got a good deal, seeing as how it came with all gauges, a clock, resistors, bulbs etc...
I was able to substitute parts on several occasions to get all my gauges working.
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Burning Brakes
Joined: Jan 2006
Posts: 876
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From: Same as our leaders Out of my mind
Originally Posted by 69camfrk
Bob, was your gauge reading all over the place or sort of not reading at all? I know my temp gauge has power, but the temp never really comes up. I replaced the sending unit with an auto parts store one with no change. I'm curious as to where others stand in relation to my problem before I start chasing gremlins.