Repro tach + Pertronix == Help!

[davepl]

My reproduction tach reads 0 with the key off.
With key on but engine NOT yet running, it reads 2150.
It reads 4800 with it running (likely around 1200).

I have the Pertronix Igniter III module in stock-looking distributor. No HEI, but its likely a similar problem.

My DVM shows 12.3 volts (engine off) at BOTH sides of the coil. I have the red wire from the ignition module in the distributor going to the + of the coil and the black to the -, and the pickup from the tach going to the neg (-) post on the coil. They're embossed so hard to get backwards, and it runs.

I've read a ton of HEI-Tach searches without much success. Sounds like a member called Necromancer can recalibrate the old tachs. People talk about a filter circuit, some argue that's only for radio interference, and so on. The catalogs for these all say "Not for use with HEI", but they just work for some people it seems. But not for me.

Most of those threads are up to 9 years old, so I have to ask:

Can someone tell me what the current state of the art is for running a reproduction tach with an updated ignition?

How can I make it work?

Many thanks,
Dave