When you install an MSD ignition, the factory ECU may not be able to distinguish when the coil fires. This is the signal that is also responsible for firing the injectors (or the tachometer), which may cause a no-run situation. These dual channel ignition adapters simulate the original coil trigger signal, thus allowing the ECU to properly trigger both the tachometer and fuel injection with the MSD DIS ignition installed. In most cases, the adapters will plug directly into MSD's harnesses. For vehicles using an MSD DIS-2 ignition, only one adapter is required. For DIS-4 applications, two adapters are required.