78 corvette tach issue
Thread Starter
Cruising
Joined: Aug 2022
Posts: 13
Likes: 2
From: Humble TX
78 corvette tach issue
I purchased this vette in June and I’ve been checking off items needing attention. The current item Tachometer. 1. Zero at idle. 2. Tach needle will move when accelerator is mashed but, will drop to zero by just backing off a tad. I have 12 volts and good ground to the gauge. I just installed a new filter…ohms checked good and replaced circuit board. Bypassed the filter…no change. The Tach was replaced at one point…2009 m date. Any ideas…new tach? Thanks
Thread Starter
Cruising
Joined: Aug 2022
Posts: 13
Likes: 2
From: Humble TX
Le Mans Master
Joined: Jun 2019
Posts: 7,649
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From: Indiana
Thread Starter
Cruising
Joined: Aug 2022
Posts: 13
Likes: 2
From: Humble TX
Thread Starter
Cruising
Joined: Aug 2022
Posts: 13
Likes: 2
From: Humble TX
Continuing issue with my Tach. Just finish installing the circuit board from Cajun Tach…same issue as the original post. 3 circuit boards, new printed circuit card, new filter. Tach was also replaced at some point prior to my purchase. T/S continues.
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Le Mans Master
Joined: Jun 2019
Posts: 7,649
Likes: 2,466
From: Indiana
Hmmm
have you applied voltage per willcox video and reset pointer to zero?
fs section will unload the tach board if needed.
luckily 78 easy to take in and out..
triple check wires going into distributor
have you applied voltage per willcox video and reset pointer to zero?
fs section will unload the tach board if needed.
luckily 78 easy to take in and out..
triple check wires going into distributor
Thread Starter
Cruising
Joined: Aug 2022
Posts: 13
Likes: 2
From: Humble TX
Tach pointer goes to zero when power is supplied. Good coil continuity from Dist to cluster, good grd, and 12 volts present at cluster connection. Replaced Dist capacitor and terminal block and ignition control module. Engine runs great.
Le Mans Master
Joined: Jun 2019
Posts: 7,649
Likes: 2,466
From: Indiana
Thread Starter
Cruising
Joined: Aug 2022
Posts: 13
Likes: 2
From: Humble TX
Thanks for the info. So I ohm checked the gauge. I read 223 ohms across the lft & rt horizontal pins in relation to the gauge. Zero values between the top pin and the lft & rt horizontal pins. My scenario different from the video. But, it does appear the gauge is defective. Their should ohm values between all the pins. Thanks for your assistance.
Le Mans Master
Joined: Mar 2004
Posts: 7,463
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From: Little Rock AR
My Vette tach acted up once but a loose connection at the filter/mount fixed it.
Lots of parts and work here. I have no idea how to fix a tach but when I did have tach problems, I sent mine to "Gary the Tachman". This is all he does. He fixed it right and sent it back to me. Done.
Lots of parts and work here. I have no idea how to fix a tach but when I did have tach problems, I sent mine to "Gary the Tachman". This is all he does. He fixed it right and sent it back to me. Done.
Racer
Joined: Oct 2018
Posts: 457
Likes: 132
From: England
Probably not your issue, but have you tried the Cajun Tach board without using the filter? When I replaced my board with the Cajun Tach one it wouldn't work with the filter still fitted, but it works fine without it.
Thread Starter
Cruising
Joined: Aug 2022
Posts: 13
Likes: 2
From: Humble TX
Finally have my tach issue resolved. Installed a new tach…now works like it should. Thanks Interpon for the video. Ohm checking the gauge itself was the determining factor of the failure.
Once again Thanks Interpon and all who chimed in.
Once again Thanks Interpon and all who chimed in.
Thread Starter
Cruising
Joined: Aug 2022
Posts: 13
Likes: 2
From: Humble TX
I needed to replace my speed/tach lens cover. While the cover was off, I removed the Tach so I can verify the serviceability of the three tach circuit boards I now have. The Wilcox (orig) Zip, and Cajun Tach all checked out good.