79 Vette Tach Question
Thread Starter
hardworkinman
Joined: Oct 2007
Posts: 507
Likes: 0
From: TN
79 Vette Tach Question
My tach recently stopped working after I got my car back from the paint shop. Does the tach work off of a fuse and if so, could that be why it's not working? I can't hardly see the fuse box, does anyone know which one it would be?
I know they were disconnecting the battery several time so I just figured they might have blown a fuse...
I know they were disconnecting the battery several time so I just figured they might have blown a fuse...
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
In the diagrahm, it looks like the same fuse that supplies the gauges also supplies power to the tach, so it they are working, then the fuse must be good. Did you check to make sure it's plugged in good at the distributor? Should be a white wire there.
Instructor
Joined: Aug 2007
Posts: 138
Likes: 0
From: san antonio Texas
some trouble shooting steps
1) bypass the tach filter, if it works replace the filter wire
2) take the speedo/tach lens off and the trim, unscrew the tach face and pull the face out, check the tach board by touching a 9v battery terminals to the 12v and coil screws, if the tach zero's out the board is still good.
3) the top left hand corner fuse "inst lap" should be checked
4) make sure the main speedo/tach wire is clipped into the back and is touching the circiut board properly. You can see if it is clipped in as it is on the left side of the tach housing behind the tach board,
2) take the speedo/tach lens off and the trim, unscrew the tach face and pull the face out, check the tach board by touching a 9v battery terminals to the 12v and coil screws, if the tach zero's out the board is still good.
3) the top left hand corner fuse "inst lap" should be checked
4) make sure the main speedo/tach wire is clipped into the back and is touching the circiut board properly. You can see if it is clipped in as it is on the left side of the tach housing behind the tach board,
Team Owner
Joined: Jul 2006
Posts: 22,154
Likes: 4,168
From: Kannapolis NC
When you turn the car off, the tach will go up to some number and stay. When you turn the key on, if the tach goes to zero, you have 12 volts and ground. If that happens, forget a fuse. The white wire coming from the distributor connects to a filter bolted to the manifold, then the other end of the filter goes to the tach. If bypassing the filter doesn't help, you need to pull out the tach (from the front) and look at the connections and the board. If the board has a burned spot, you probably need a new one. If you do, get one that is pre-calibrated for the 78-79. Willcox has one for around $75.
Thread Starter
hardworkinman
Joined: Oct 2007
Posts: 507
Likes: 0
From: TN
When you turn the car off, the tach will go up to some number and stay. When you turn the key on, if the tach goes to zero, you have 12 volts and ground. If that happens, forget a fuse. The white wire coming from the distributor connects to a filter bolted to the manifold, then the other end of the filter goes to the tach. If bypassing the filter doesn't help, you need to pull out the tach (from the front) and look at the connections and the board. If the board has a burned spot, you probably need a new one. If you do, get one that is pre-calibrated for the 78-79. Willcox has one for around $75.
Team Owner
Joined: Jul 2006
Posts: 22,154
Likes: 4,168
From: Kannapolis NC
It won't be the filter. You'll have to get the 12 volts and ground to the tach first. If it never moves off zero when you turn the power off, sounds like the tach movement is stuck. I'd take off the plastic lens and gently move it. It should bounce up to around 800 rmp with the switch off.
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Instructor
Joined: Dec 2005
Posts: 218
Likes: 0
From: Waverly NY
Did the paint shop disconnect any ground straps to the engine? Both gauges are engine related and need a good ground to work properly. Sometimes just moving the old ground straps causes them to break.
Kipp
Kipp
