I'm installing Autometer 5" Monster Tach in my 240Z. As some of you may know, the stock Tach runs off of positive pulses from the coil. Whereas the Autometer runs off negative pulses. OK, that's easy enough. Problem is that the stock tach servesa dual purpose. It not only reads the pulses on the coil, it also is a necessary part of the circuit. Removing the tach prevents the engine from running. So, in my quest for a solution, and after a few minutes of staring at the wiring diagram, I have a few questions. First, it seems quite easy to bypass the stock tach and just run a wire directly from the ballast resistor to the positive coil terminal. Then, while I'm at it, why not just remove the ballast resistor altogether? But, before I attempt this (I haven't had the time yet), I wanted to get some opinions as to whether or not this is a good/bad idea and why. What's the purpose of the ballast resistor anyway?