Installed new coil, now the tach acts funny

Just as the title says, I installed a new ignition coil, and now the tach is acting funny.

Fresh 318 build, electronic ignition, new Edit: Auto Meter tach. Old coil was unbranded and who knows how old, new coil is an MSD Blaster 2.

Here's the deal. I literally removed my old coil and installed a new one. That's it. That's all I did. The tach was reading perfectly before, and now it reads zero upon first startup. It'll register some RPMs when I pop the gas pedal, but still seems "off." Driving down the road, the tach will register RPMs, but seems 500-1000 below what they should be. The new coil came with a ballast resistor, initially I didn't install it until I noticed the tach acting like this. I installed the new resistor and the problem persists. The engine is running the best it ever has, but now I've got the tach issue.

What did I miss or not do correctly?