The Module Selectors can also be used with an MSD Timing Control. By plugging the Selector into a retard module socket, you can acti­vate different retard amounts at select times. This is a great feature for engines being upgraded to a multi-stage nitrous system. With the addition of an RPM Activated Switch, you can use the Two Step to activate a shift light at different rpm.The Module Selectors must be used with an MSD Soft Touch Rev Control or a Timing Controller with a high-speed retard module. No rpm or retard modules are supplied.