My Westach still works, but acts differently, after installing Pertronix ignition in my truck. The Pertronix triggers the hot side of the coil instead of switching the ground side like the points system does. I believe I still have my tach connected to the + and - terminals on the coil. At lower RPMs it seems to read low now, but when it gets spun up it seems to come into line to where it should read. I’ve double checked it with an inductive pickup tach on my multimeter. I also find that after startup the tach won’t move until I rev the engine a little bit, then it’ll settle in and show RPM, but a little low as mentioned.