The MSD Module Selectors allow you to choose two or three different rpm limits that can be activated at different times. With this ability, the possibilities are endless.As an example, well use a drag car with a Three Step Module Selector plugged into the rpm socket of a 7AL-2 Ignition. The different rpm modules are activated when 12 volts are applied to a corresponding wire. By connecting one wire to the line-lock circuit, one module will be activated during the burnout. This helps keep tire temperatures consistent. When the line-lock button is released, the limit turns off. When youre on the starting line, you can activate the second limit through the clutch or trans switch. This provides a steady and consistent rpm for firm holeshots every time. When no modules are selected, the remaining high limit is active to protect the engine in the event of driveline failure. The Two Step works the same, but only with two different limits.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. MSD RPM Controls Two Step Module Selector 8739 Allows User To Switch Between 2 RPM/Timing ModulesSet A Different RPM Limit For The Launch/OverrevImproves Consistent HoleshotsMust Be Used w/MSD Soft Touch Rev LimiterMust Be Used With MSD Timing ControlNo RPM Or Retard Modules Are SuppliedPit Stop USAoffers MSD Ignition RPM Controls Two Step Module Selector 8739 at low everyday prices. Be sure to check out all of the products from MSD Ignition including MSD Ignition Parts and Accessories, MSD Ignition Parts and Accessoriess, MSD Ignition RPM Module Selectors.