Factory tach +Electronic Conversion Module

[custom10nut]

My factory tach is reading 200 rpm at idle. I just recently replaced my printed circuit board, and prior to that my tach worked fine.
I do have a Mallory Electronic Conversion Module, in place of points.
Again I say, the tach used to work fine.
But could the ECM be causing my issue? If it is cause, is there a filter like those used by people running HEI distributors?

[davepl]

I've seen multispark ignitions causing it to read high, but never low. How well does it track RPM? Like if you go up to 2000, what does that tach read?

Is it connected to the tach output of the Mallory (if it has one) or the coil?

[custom10nut]

The ECM is just in place of the points, so the tach wire runs off the coil.
The thing that has me scratching my head is that everything was fine before. I will hook my multimeter up to see how the other rpms read.