This will correct the operation of most tachs and fuel injection pump relays that do not work directly off of the MSD Ignitions 12 volt square wave tach output terminal. If, after installing an MSD In Control, your tach, fuel pump relay or electronic fuel injection (in foreign vehicles) does not operate correctly, your application may require a Tach Adapter. This is due to the trigger signal not being strong enough to trigger both the MSD and the factorys components.