Noticed a lot of folks have asked this question at one time or another on MSD Ignition modules having the tach output. It is official as of today that you DO NOT have to use an MSD Tach Adapter with a factory Mustang gauge. I used a tach adapter thinking I needed it and my tach bounced all over the place. I attempted to use the tach output directly from the MSD ignition module to the tach and then it started working properly. Now I have an adaptor that will be used for an aftermarket tach I guess. Unless I buy an Autometer, because they state in their directions that they do not need an adapter. This should help anyone searching this in the future.