Tach question?????????????

[porman1]

Have just purchased a used 8K tach date coded '76 to install in a '79SC.(new engine redlines at 8K old tack stops at 7K)........the wiring is the same but it does not not operate using the HPX tach signal. The orignal does. Does anyone know if the earlier tack runs on a 12V square wave signal?

Thanks for your help.

Erick

[Early_S_Man]

The '76 tach used ground pulses from the points to trigger, and was an approximate 6 Volt peak-to-peak signal.

The '78 and later tachs used a trigger generated by the 6-pin Bosch CDI-units at terminal 'TD.'

[porman1]

Thanks for the input........now off to find a solution.

Thanks