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1975 tach problem

Old Nov 7, 2009 | 11:59 PM
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Default 1975 tach problem

1975 tach. Goes from zero at idle to negative numbers as rpm increases. Any ideas out there?
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Old Nov 8, 2009 | 12:57 AM
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Sounds like a 'electrical ground' issue. Any loose wires?
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Old Nov 10, 2009 | 07:17 PM
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a little more info..... The tach sits at zero with no power or key in the ign. When I start the engine, the tach moves toward negative numbers(towardthe 7000 rpm mark) As the engine speeds up, the tach moves toward 6000then 5000.

Still looking for help. No obvious loose wires. Has anyone out there seen this before????
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Old Nov 10, 2009 | 09:12 PM
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Somebody brought this up awhile back but can't remember what the outcome was. I believe Willcox chimed in about it.
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Old Nov 11, 2009 | 12:28 AM
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Yes I've seen this before! You have a board issue! The only way for the tach needle to go to zero when the key is turned on is for it to have power and ground. The only way the needle will move is for it to have a input signal. If the needle is moving backwards, you have an issue with the board itself.

I don't have the links up for the 75-77 tach boards just yet!

The new 75-77 boards were completed last week for final testing and the link should be up real soon! Actually in a matter of days.

Willcox
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