The MSD Shift Light will turn on to "remind" you to shift when the engine reaches your specified rpm. You select the rpm using the same plug-in modules that are used with your MSD Soft Touch Rev Control. The Shift Light features a bright cluster of LEDs making it easily visible, even in bright daylight. The light will also turn on for a second or two when the ignition switch is first turned on to inform you that the light is functioning properly. The Shift Light will work on 2, 4, 6 or 8-cylinder engines and will plug directly into the tach output on MSD 6, SCI, 7, 8 and 10 Series Ignitions or can be connected to the negative coil terminal when used with points or inductive-type ignitions. The MSD Shift Light is 4.5"L x 3.5"H with a 1.5" diameter lens. No rpm modules are supplied.