This MSD Ignition tach adapter is for use with magnetic pick-up units. The tach adapter will correct the operation of most voltage triggered tachometers that do not work directly off the tach output. If you are connecting a tachometer to an MSD Ignition or your application is equipped with electronic fuel injection then you may need to use this Tach/Fuel Injection Adapter to ensure correct operation. This Adapter will correct the operation of most tachometers and fuel injection pump relays that do not work directly off of the MSD Ignitions 12 volt square wave tach output terminal terminal of the MSD Control.