I just replaced the circuit board on the gauge cluster. And I traced the brown wire from the harness to see that it was hooked up to the negative side of the coil. This means that the tach itself is bad I'm guessing? Also I read that if u have an hei that it can mess up the tach without a filter on it. I'm sorry to sound like such a novice, but how do I know if I have an hei? Cause I hate to buy a new tach and instantly mess it up. Thanks