First, Welcome to the Shark Tank!!

Do any of the gauges work? The tach board is separate from the console gauge board, so if all of them are not working, I would be looking at a wiring problem(ground), or possibly a fuse/fuse link.
I can send you a wiring diagram, if that would help. It does have the schematics for the circuit boards, I think...
It does have the console gauge board. The tach board is actually mounted on the back of the tach.
P/M me with an e-mail address, and I'll shoot ya the diagram.

A lot of times, when the tach doesn't work, it is the filter, by the dist. If you unplug it, and the tach works, the filter needs to be replaced. It is in/on the white wire, and supplies the rpm signal to the engine computer.Adams' Apple2006-11-13 20:26:46

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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

This may be silly, but...have you checked the fuses? The tach normally sets at 3-4000 when the key is off, I think. When it is powered(key on) it should go down to read correct RPMs. The other gauges not reading correctly would tend to support a no power/ground issue. Then again, it could be a problem in the ign. switch.
I'd suggest a good check of all the fuses with a meter/test light, before condemning the boards. As I said, the two gauge packs use separate boards...hard to believe they would both go bad at the same time, or that one bad one would effect the other.

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

have you taken the console out...then you can check with a multimeter or maybe you can already see if some on the "wires" are broken on the circuit

the console with the temp, oil , clock etc gauges is quite easy to get out... one big plug on the back and don't forget the one on top ( light on console)


art-corvette

[QUOTE=Adams' Apple] First, Welcome to the Shark Tank!!

Do any of the gauges work? The tach board is separate from the console gauge board, so if all of them are not working, I would be looking at a wiring problem(ground), or possibly a fuse/fuse link.
I can send you a wiring diagram, if that would help. It does have the schematics for the circuit boards, I think...
It does have the console gauge board. The tach board is actually mounted on the back of the tach.
P/M me with an e-mail address, and I'll shoot ya the diagram.

A lot of times, when the tach doesn't work, it is the filter, by the dist. If you unplug it, and the tach works, the filter needs to be replaced. It is in/on the white wire, and supplies the rpm signal to the engine computer.[/QUOTE]

Hey bro can ya fire me that diogram? My tach haint nair worked. I'm a workin on da C5 raight now but hit haint gonna tak me all winnter.

                                    thankee! Tux...

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no...

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Just a quick note on the O/P reading at MAX - mine did the same thing and it was the sending unit. BTW - if you go to the stupid auto parts stores, they will often look up the Vette and give you a sending switch (for an idiot light). The sensor for the guage looks like a small beer can.  Best to take in the old one to compare. 

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C3: 1979 Corvette Coupe, Auto, L-48, Red/Doeskin (my wife's fave);

[QUOTE=sfindlan] Just a quick note on the O/P reading at MAX - mine did the same thing and it was the sending unit. BTW - if you go to the stupid auto parts stores, they will often look up the Vette and give you a sending switch (for an idiot light). The sensor for the guage looks like a small beer can.  Best to take in the old one to compare.  [/QUOTE]

Mine did OP gauge did the same thing and you are dead on about the auto parts dude. I went to a Car Quest store and that is exactly what happened. Unfortunitly I didn't take the 1st one out prior to going because I was out of town when it decided to start puking oil out of the end. So I had to drive back to the store and they were out of the right one. He was good enough to make a few calls for me and locate one for me so it worked out.


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The tach board (which is a pc board) is often the culprit - but not always. It was a gamble in my C3 as well as a few friends - we were 100% successful. In every case, the tach seemed to "float" around a certain RPM and bounce a litttle in reaction to RPM. Replaced the tach board and worked like new. The tach board is a $60 investment and can be replaced by taking the tach out from the front of the dash. No contortionist work under the dash for this one....

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Thanks for the info and advice. I will change the OP sending unit and see if that makes a difference. Not sure if the one on the car is original since it does not look like a small beer can. Wish I could find a picture of one. Any ideas? Can't find one on Mid America or  Corvettte America.

I had a similar problem with my tach, and replaced the board.  It then did much more, but was still odd and wrong.  I had to have the coils in the tach itself replaced as well.  So I had a two part hit.