I hate to even ask this, but I am having a problem with getting my aftermarket tach to work properly on my 72 K5. I run a 350 SBC with a Mallory Unilite distributor, and Holley Pro-Jection 2D system. I've contacted both Mallory and Holley tech departments to see if I need to use some sort of capacitor/resistor off of the negative coil terminal to "condition" the signal so the tach works. They both said that their systems do not affect the factory tach wiring. I also have tried about 3 different tachs with the same results. My question is how is the factory tach wired in? I have always assumed black to ground, red to switched 12V source, green to negative coil terminal (for inductive style distributor), and white to dimmer switch. Any help on this would be mucho appreciated.