My Tach doesn't work at all.....all other gauges good to go. I have lived with it for a few years and want it working.
Is it no doubt a "board" issue and if so is replacement of the whole assembly the only option ?
Cheers and thanks for any and all replies.

 

Could be the board, but check the main plug in connector on the back of the IP first. You can buy just the circuit board from any of the Vette parts guys.

http://www.zip-corvette.com/Zip/prod...4E2DE75F6D7012

Here's a how-to article
http://www.corvettemagazine.com/2005.../tach-lead.asp

 

Yes, it is more than likely a circuit board issue. It is an easy fix with basic tools and a bit of patience. The tach can be removed by removing the speedo/tach lens. Then using the correct allen wrench, remove the black plastic bezel that surrounds the speedo/tach. Then remove the three hex head screws that secure the tach to the main housing for the speedo/tach. Then pull on the tach and it will release from the tension clips that supply power to the tach. If you see a burnt spot on the circuit board it is more than likely bad. The three electrical connectors that are secured to the main housing supply, 1.) power when the key is turned on, 2.) a ground, and 3.) the reference wire from the distributor. Check to make sure that these are correctly working with a test light and/or a volt/ohm meter. Use a process of elimation to determine which one is which one. On the side of the distributor cap ther is a square area that comes off the side of the cap. The tach wire should be connected to the left port , the right port is the power to feed the coil,etc. These areas are marked "TACH" and "BAT" . Often times there is a filter that is bolted to the intake manifold and allows the wiring from the main harness to be connected to the filter and the other end of the filter is connected to the distributor cap. In a perfect world, your filter should be connected this way, but usually the wires are broken off and often times the filter is removed and has been discarded. The wire you are looking for out of the main harness is often times a white wire with a brown connector clip. And it is designed to only go in the area of the distributor earlier described. If you do need a tach board, they are simple to install by following the instructions and as I have been told by the guy who builds them is that the filter is not needed if missing or damaged. Last but also possible is that the printed circuit board on the main dash panel is damaged or the connector is not seated correctly or the copper portion of the circuit board that contacts the connector has been bent back or not positioned correctly. If you test the three points where the tach gets power, ground and reference signal, then the printed circiut board for the main panel is ok. Good luck and don't sweat it.

 

On your tach circuit, you will need to verify the following:

Make sure you have 12 volts to the tach

Make sure you verify the Tach ground

Make sure you verify continuity from the tach wire on the connector to the distributor.

Inline on our car there is a tach filter, this filter is held in place with one bolt to the intake manifold. If you do not have continuity from the connector to the distributor, un-plug the tach filter from the system. See if you have continuity from the dash connector to the plug where the filter plugged in. If you do have continuity to this connector then plug this connector to the “tach” connector on the distributor bypassing the tach filter. Now plug in the connector and see if it works. If this works inspect the filter to see if the wire is broke at the capacitor, if it is you can try to place a drop of solder in the capacitor to get the filter working again. This can be hit or miss. If the filter is bad we do carry a replacement style on the web site.

Testing without the filter will not hurt the tach in any way shape or form. If the tach works when you do this you need to replace or repair the filter.

If you have power at the tach and a verified ground with good continuity from the distributor to the tach and it is not working you have a board problem more than likely. If you want to test the tach by doing a hard wire test the help page listed below will tell you exactly how to do this. It is the same test we suggest you do before installing a tach with a new board in the car just to verify the tach is working properly.

I have a page on my web site that will help you in this repair: (and has the hard wire test). http://willcoxcorvette.com/repairand...lp.php?hID=252

I also have a page on the site on how to remove the tach from the car at this link:
http://willcoxcorvette.com/repairand...lp.php?hID=146

Should you need the tach board, I have them listed in the Forum Special section under this link and these boards are pre-tested and calibrated before we send them out. http://willcoxcorvette.com/advanced_...&keywords=tach If you enter the current sale discount code on check out, you will receive an additional discount on this item too. This sale code is DRWH3A and must be entered when checking out on the site.

On your printed circuit, the top wire on the tach side is your ground, the second wire down is the signal wire from the distributor and the third wire from the top is the power wire. Not this is if you were looking at the back of the tach with it sitting on our lap. So the wires in the car if you were facing the connector when un-plugged go to the passenger side top wire. This is the tach ground. The passenger side wire second from the top is the square signal wire from the distributor, and the third one down on the passenger side of the plug is the 12 volts to the tach.

I hope this make sense. . .

Now pull the tach, test your wires and if this is not enough info either post again or email me direct at Willcoxcustomerservice@willcoxcorvette.c om.

Willcox Inc.

Here is the printed circuit board for the tach and speedo showing the wires above.

 

Hey torture and its really not that bad with the redesign of the 78 dash. The suggestions above by Wilcox and grandmaster hit the target. I just did my 78 back in the fall. Vendors report that 95% of the time, its the board but as Wilcox points out, do some circuit tests to ensure you've got juice to the board. I just wrapped up an article for a Corvette magazine on this topic and if interested, PM me and I'll send.