Temp Gauge Not Working
Thread Starter
Intermediate
Joined: Nov 2008
Posts: 38
Likes: 0
From: New Jersey
Temp Gauge Not Working
The other day while driving my 1977 Corvette, I noticed the temp gauge needle fluctuating rapidly. Before this the gauge worked fine.
Upon returning home the gauge stopped working. The needle is resting in the lowermost position which is about 100 degrees.
Up to now I have replaced the sending unit. This did not work.
Then I grounded the wire that connects to the sending unit to the block while the ignition was in the on position. No movement.
Before I proceed further can someone advise me on what to do next?
My next move was to remove the center gauge cluster. But this appears to be a big job and I am not sure how to do it. The only thing I can think of is that maybe one of the wires on the back of the gauge fell off or something to that effect. I think the gauge is still good because the needle is in the lowest part as if the car is turned off.
If I do need to remove the center cluster, can someone advise me on how to do it?
Any help is greatly appreciated. Do not want to drive the car without a temp gauge.
Thanks guys.
Upon returning home the gauge stopped working. The needle is resting in the lowermost position which is about 100 degrees.
Up to now I have replaced the sending unit. This did not work.
Then I grounded the wire that connects to the sending unit to the block while the ignition was in the on position. No movement.
Before I proceed further can someone advise me on what to do next?
My next move was to remove the center gauge cluster. But this appears to be a big job and I am not sure how to do it. The only thing I can think of is that maybe one of the wires on the back of the gauge fell off or something to that effect. I think the gauge is still good because the needle is in the lowest part as if the car is turned off.
If I do need to remove the center cluster, can someone advise me on how to do it?
Any help is greatly appreciated. Do not want to drive the car without a temp gauge.
Thanks guys.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Ignition ON, engine OFF: remove wire from sender (OPEN circuit) and meter needle should be at one end of the scale; ground the sender wire to the block (SHORT circuit) and meter needle should be at the other end of the scale. If that test works OK, then the meter is fine. If that test shows no needle movement, then one of two things is your problem: the 12v. line to the gauge has had a break in it (or bad connection); the meter circuit has failed--probably a termination connection on a fine coil wire has fatigued.
The fluttering you saw on the gauge was the [defective] wire [wherever it turns out to be] finally losing its 'grip' and breaking the connection. My 'guess' is that the 12v. power feed to the gauge was lost.
The fluttering you saw on the gauge was the [defective] wire [wherever it turns out to be] finally losing its 'grip' and breaking the connection. My 'guess' is that the 12v. power feed to the gauge was lost.
Thread Starter
Intermediate
Joined: Nov 2008
Posts: 38
Likes: 0
From: New Jersey
Just did the test as described above. Turned ignition on, engine off. With wire on sending unit gauge was at lowest level. Disconnected wire and shorted to block, no movement.
Put a digital voltmeter across gauge at rear of gauge. Meter read -17 volts!!! I measured at the three o'clock and nine o'clock positions.
Should the voltage be this value?
Put a digital voltmeter across gauge at rear of gauge. Meter read -17 volts!!! I measured at the three o'clock and nine o'clock positions.
Should the voltage be this value?
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Where in the world did you get that picture above,thats about as wrong as you can get. 
Go to the Willcox site and to the help section , he has an accurate pic with the proper washers and all.
Go to the Willcox site and to the help section , he has an accurate pic with the proper washers and all.
Thread Starter
Intermediate
Joined: Nov 2008
Posts: 38
Likes: 0
From: New Jersey
Roger thanks for the heads up. I found a picture on the wilcox website and I think I found the problem. It appears to be a break in the wire from the sending unit to the gauge.
This is what I did.
At the back of the gauge I shorted the ground and temperature gauge sender terminal. The gauge moved to the uppermost position.
Then just to satisfy my curiosity...
I connected a wire to the engine block and ran it to the back of the gauge on the temperature gauge sending unit terminal. Once again the gauge needle moved from the lowermost position to the uppermost position.
Therefore, it appears that there is a break in the wire from the engine compartment.
OR...
There is a break on the printed circuit board.
This is what I did.
At the back of the gauge I shorted the ground and temperature gauge sender terminal. The gauge moved to the uppermost position.
Then just to satisfy my curiosity...
I connected a wire to the engine block and ran it to the back of the gauge on the temperature gauge sending unit terminal. Once again the gauge needle moved from the lowermost position to the uppermost position.
Therefore, it appears that there is a break in the wire from the engine compartment.
OR...
There is a break on the printed circuit board.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You made a good diagnosis. It appears to be a break in the sensor signal line [based on your results]. A 'failed' foil line on the circuit board or a broken sensor wire are the possible culprits.
Thread Starter
Intermediate
Joined: Nov 2008
Posts: 38
Likes: 0
From: New Jersey
Thanks!!
Since I have the cluster out, I am going to replace the low fuel bulb too. The cluster was quite easy to remove.
This is the picture that I found that has all of the gauge cluster connections.
http://willcoxcorvette.com/instructi..._schematic.pdf
Scroll down a bit and you will find the printed circuit.
Hope this helps someone else with that same problem.
Since I have the cluster out, I am going to replace the low fuel bulb too. The cluster was quite easy to remove.
This is the picture that I found that has all of the gauge cluster connections.
http://willcoxcorvette.com/instructi..._schematic.pdf
Scroll down a bit and you will find the printed circuit.
Hope this helps someone else with that same problem.
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Former Vendor
Joined: Aug 2006
Posts: 76,656
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Ooglie.. ping the wire for continuity from the cluster plug in to the end where it connects to the gauge. My bet and from what you described is that the sending unit wire is broken. Check right at where the wire runs in to the main harness and you'll have to have a tester you can pierce the wire with. Not a big deal but you should be able to find your short.
With the needle resting on the 100 degree position it sure sounds like you are missing input ohms to the gauge.
If you grounded out the gauge and and received a hot temperature then it also appears as if the gauge is working just fine!
I'll be online later tonight too.. but here is the picture Roger is talking about.
http://willcoxcorvette.com/repairand...lp.php?hID=284
Willcox
With the needle resting on the 100 degree position it sure sounds like you are missing input ohms to the gauge.
If you grounded out the gauge and and received a hot temperature then it also appears as if the gauge is working just fine!
I'll be online later tonight too.. but here is the picture Roger is talking about.
http://willcoxcorvette.com/repairand...lp.php?hID=284
Willcox
Last edited by Willcox Corvette; Jun 14, 2010 at 03:21 PM.
Instructor
Joined: Mar 2009
Posts: 209
Likes: 1
From: Denver CO
Hey gentlemen I am having a similar issue on my 74', when i key on the power the needle on the gauge jumps a bit, so I know its getting power. I replaced my sending unit and the wire from the unit to the gauge. Still I have no response from my temp gauge other than the flick on power. Was considering sending it into Ecklers for their gauge restoration service... but could it be anything else. Or am i right in guessing that my gauge is bad?
Thread Starter
Intermediate
Joined: Nov 2008
Posts: 38
Likes: 0
From: New Jersey
Ooglie.. ping the wire for continuity from the cluster plug in to the end where it connects to the gauge. My bet and from what you described is that the sending unit wire is broken. Check right at where the wire runs in to the main harness and you'll have to have a tester you can pierce the wire with. Not a big deal but you should be able to find your short.
With the needle resting on the 100 degree position it sure sounds like you are missing input ohms to the gauge.
If you grounded out the gauge and and received a hot temperature then it also appears as if the gauge is working just fine!
I'll be online later tonight too.. but here is the picture Roger is talking about.
http://willcoxcorvette.com/repairand...lp.php?hID=284
Willcox
With the needle resting on the 100 degree position it sure sounds like you are missing input ohms to the gauge.
If you grounded out the gauge and and received a hot temperature then it also appears as if the gauge is working just fine!
I'll be online later tonight too.. but here is the picture Roger is talking about.
http://willcoxcorvette.com/repairand...lp.php?hID=284
Willcox
Raider...
My guess is that it is not the gauge but a continuity problem from the sending unit to the gauge. I went through the trouble of removing the gauge cluster and conducting a few tests with the back of the gauge exposed. Without removing the gauge cluster and grounding the sending unit wire, I saw no movement in the gauge. Since I did remove the cluster I was able to see the gauge was working.
This allowed me to narrow down the break in the circuit.
