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RPM Tachometer fault

Hi all my problem is my rpm tacho goes all the way past redline as far as it can go on the tacho face and stays there. with the ignition on but engine not running or engine running makes no difference. i pull the green sender wire off negative side of coil and makes no difference. the black wire has a good ground. any idears lads. thanks john

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Comments

It sounds like a capacitor inside the tach has gone short, allowing DC to get to the movement.

Open the unit and meter all the caps.

You could also try adding an external cap between the green wire and the coil -ve. You'll need somehing similar to a 400volt 1 microfarad greencap capacitor, not an electrolytic.

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T

My Shed

Holdenpaedia, they're the brakes Mate.

Rework (resolder) the tacho's circuit board.
Sounds like you have a bypass somewhere.

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