Installed new coil, now the tach acts funny

Well this gets even stranger.
As far as I am aware, the only wires going to the dist on Chrys Electronic ign dizzies are the p/up wires. So, AM is saying to hook the tach wire to one of these?
For a start, never heard of any aftermarket tach that gets a signal from the p/up.
And the p/up output is a sine wave, not a square wave??