78 Tach Board Location?
Thread Starter
Intermediate
Joined: Aug 2007
Posts: 44
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From: havelock nc
78 Tach Board Location?
I am trying to change the tach board in my 78 vette. I removed the speedo/tach gauges and its not on the back of the gauges. Is it located inside the tach or some where else? 
Pro
Joined: Mar 2007
Posts: 727
Likes: 113
From: Austin TX area
I had to change all my light bulbs on the instrument panel and the center panel. There is a little board on the center panel. This board has a bulb also. After I change all the bulbs and put it back together I did not take note as which spot this board came out of. My tach would bounce and my gas gauge would not register. I moved the board over and everything work as it should. 
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
You don't need to remove the tach/speedo ***'y to get to the tach board. Remove the front clear bezel, remove the six screws holding the black plastic surround around the tach and speedo. Remove the three screws holding the tach and pull the tach forward. This will disconnect the tach and tach board together. Turn the tach around and you'll see three nuts holding the tach board to the tach. You'll probably see a burned spot on the board too, if it's not working. Make sure you get a board calibrated for a 78/79 or it won't read correctly. Willcox has them for $75 plus shipping.
Thread Starter
Intermediate
Joined: Aug 2007
Posts: 44
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From: havelock nc
Thanks for the Info. I did it the hard way, I took the speedo/tach housing out from behind the stearing wheel. I thought it was behind the instrment cluster. I did as you said and found it conected to the tach. I had it tested and it was bad. I ordered a calbrated one for Zip auto parts. I hope this fixes my problem. 
Thread Starter
Intermediate
Joined: Aug 2007
Posts: 44
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From: havelock nc
Install a new calibrated Tach board today and the tach works like champ. The only problem I have now is the lights in the speedo/tach display no longer work. I must of damaged the rear circut board when I took out the speedo/tach assembly. (Just my Luck) Has anyone ever hard wired the lights to bypass the circut board or do I need to spend $100. with shipping for a new board?
Le Mans Master
Joined: Oct 2005
Posts: 6,247
Likes: 471
From: Glen Allen, VA
I had exactly the same problem with the lights not working after taking the tach/speedo cluster out. I wound up taking the cluster back out a second time and found exactly what you mentioned, 2 of the circuits on the printed circuit board were touching, causing a dead short. A dab of super glue to hold the circuit down and carefully reinstalling the cluster the 2nd time has had it fixed ever since.
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Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
The contacts where the wiring plug connects to the flexible circuit could also be loose or corroded. Make sure you have the dimmer turned up before you take it back apart, just in case. It would suck to take it all back out and find out you had the dash dimmer down. Good luck.
Melting Slicks
Joined: Apr 2004
Posts: 2,008
Likes: 38
From: Space Coast Gator Territory
The filter is mounted on the intake manifold on the drivers side of the distributor. For someone else reading this, you can test for a bad filter by removing it from the system and plug the tach wire directly into the distributor. Just plug the wire in next to the power lead on the distributor. If the tach works, you need a new tach filter. This was my case, but I didn't check it before buying a new circuit board, so I'll have both parts new.
BTW....after replacing the circuit board you may need to re-orient the needle to the face. The needle has a small hole in the center axis that fits over a fine needle from the electronic mechanism. Put you glasses on, I could barely see it with my extra eyes.