Installed new coil, now the tach acts funny

67Dart273 said
You need to make certain that "whatever color" that the power wire from the ballast goes to coil +
And that "whatever color" the coil - goes to the ECU

Something you might try "shot in the dark"

Unplug the regulator and see if the tach works

With everything connected normally

With the engine running "fast idle" Check charging voltage at the battery. With the engine warm and the battery "normalized" you should see 13.8--14.2

If so turn on the headlights. Heater if you have it. Voltage should not drop much, not below 13.2--13.5

Now, turn your meter to AC volts. Measure right at the alternator output stud with engine still running on fast idle. You should have a very very low reading, almost zero. I would say over .3V (3/10 of 1 volt) is too much. This is AC ripple caused by bad diode(s) etc.

If you have "anything" for a radio supression cap, install at the coil+ to ground.

Well here's an update.

Unplug the regulator and see if the tach works
Tach does not work at all with regulator disconnected

With everything connected normally

With the engine running "fast idle" Check charging voltage at the battery. With the engine warm and the battery "normalized" you should see 13.8--14.2
Battery voltage was 13.83 and climbing

If so turn on the headlights. Heater if you have it. Voltage should not drop much, not below 13.2--13.5
Headlights only. I have no heater, no radio, nothing else to add load. Voltage 13.42

Now, turn your meter to AC volts. Measure right at the alternator output stud with engine still running on fast idle. You should have a very very low reading, almost zero. I would say over .3V (3/10 of 1 volt) is too much. This is AC ripple caused by bad diode(s) etc.
I don't quite know how to measure at the output stud, so I tried several configurations. I tended to get 2 readings: 32-33 volts and/or 0.6 volts. I'm guessing the 0.6 volt reading was the configuration I was going for.

If you have "anything" for a radio supression cap, install at the coil+ to ground.
Radio suppression capacitor is connected to coil positive.

The fellas at the parts store "loaned" me a couple different ignition modules so I could perhaps troubleshoot my current one. The only ones they could source were the 4-pin and 5-pin chrome boxes. I have a 4-pin orange box. My car started after lots of cranking on the 5-pin box, but the tach performed even worse. No start at all on the 4-pin box.

I'm going to contact AutoMeter one more time via email so that I have this all in writing, but I'm pretty sure I'm giving up on at least this particular model.