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, let's 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 is 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 and when the line-lock is released, the limit turns off. When you're on the starting line, you can activate the second limit through the clutch or trans switch. This provides you with 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 PRM 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.