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Tach and conversion to negative ground from positi

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ynotme2

Senior Member
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Everyone,

Sorry to keep asking a ton of questions but.... When my guy converted my car to a negative ground car and intalled the electronic ignition system he told me about the tach. The tach works but the reading looks all wrong. High at times then maybe low. He said that I would have to get it adjusted. What does that mean. The tach works but the readings look wrong. For instance at idle it show 6000 rpm. What should I do? Send it out for a rebuild?

Thanks

Tony
 
Tony, I did a search and came up with a start point for you. SEE THREAD: "...64 BJ8 Series I Tach problems..." using the search function. This covers several problems associated with tach malfunction/fix action(s).
 
The wire that runs from the ignition switch to the distributor and electronic ignition system loops through the back of the tachometer. When I added the pertronix ignition, I had to run the loop through the back of the tach a second time (2 loops) to get the tach register at all. For some reason my tach does not pick up the signal with one loop. And if you convert to a negative ground, I believe the loop (s) need to run the other direction than for a positve ground system. To get a 2nd loop, I had to splice in a smaller guage wire so that it would fit a second time. I think I used 18 g. speaker wire, just a short 3 inch piece that a spliced into the ignition/dist. wire just to fit through the small space for the loop at the back of the tach. Also inside the tach there is an adjustable dash pot to adjust the tach. You can take off the back of the tach (the case) and drill a 1/2 inch hole that lines up with the dash pot. Then put the tach back together, install it in the dash, and it can be adjusted with a small screw driver while the engine is running, just by reaching up under the dash. If the tach does not still read correctly, you may need to replace the .22 m F capacitor inside the tach. These seem to go bad with age. Finally, make sure the tach is well grounded. Good luck
 
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