This Rev Control plugs directly into a special Weathertight Connector on the MSD 6-Offroad Ignition Control. It allows you to set an rpm limit that will save your engine from over-rev damage in the event of driveline failure, slick spots on the trail or missed shifts. The Soft Touch rev limiting function is quick and smooth with no harsh backfires or roughness. This is accomplished by randomly dropping the spark to individual cylinders, then firing them on the next cycle to prevent fuel from loading up in the cylinder. The rpm limit is adjustable with special waterproof RPM Modules (4,000, 6,000 and 8,000 RPM modules included). Like the 6-Offroad Ignition, the Rev Control is completely potted with ResTech compound forming a waterproof seal over the circuits. Weathertight connectors provide locked and sealed connections. NOTE: Must be used with the MSD 6-OffRoad Ignition. OBD II and CARB Approved per E.O. D-40-29 with PN8738