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 In. L x 3.5 In. height with a 1.5 In. diameter lens. No RPM modules are supplied.