Pertronix tach signal

[davepl]

I have a Pertronix III module in a stock distributor body. I have the tach hooked up to the negative side of the coil. The first tach I tried didn't work with it at all, but a second one of unknown origin (but still a repro - hope it wasn't NOS!) did work.

I still think it reads high, and my theory is that the Ignitor III does multi-spark at low RPM, which fools the tach that can only see the coil.

Normally I'd think if you had an external ignition box that did multispark you would have a tach wire output that was only triggered once per cyl, but there is no such tach wire on the little module, so...

Is there a solution? If its multispark throwing it off, no amount of tach filtering is going to fix that.