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.