Tach signal

["Greg Wilkinson" <gregwilkinson@adelphia.net>]

Greetings All,
        I'm installing an electronic ignition system in my '67 BJ8. The ignition
control box has a 12 volt square wave output for the tach. I have no idea
what type of signal the original tach can stomach(probably made before
square waves were invented). Besides the conversion to negative ground is
there any other modification I need to make to the tach? Full system is a
pertronix ignitor in a Mallory distributor, Jacobs Pro street ignition with
65,000 volt coil.

Thanks,
Greg