These RPM-Activated Switches will perform a variety of different functions from turning on a bulb or solenoid to activating an MSD Timing Control at a desired rpm.The RPM-Activated Switch, PN 8950, has two activation wires; one to ground a circuit and the other to open a circuit. Simply plug in an rpm module and wire the Switch to the circuit you want to activate. When the engine rpm reaches that amount, the circuit is activated and will remain on until the rpm falls below that amount.The RPM Window Switch, PN 8956, has two rpm adjustments; one to activate a circuit, while the other deactivates the same circuit. Removing ground to a circuit is a great feature to deactivate nitrous before the engine's rev limit is reached. Both Switches can be used with stock inductive ignitions or an MSD Ignition and can handle up to 1.5 amps. No rpm modules are supplied so they must be ordered from the selection of Modules shown on page 124. For use on 4, 6, or 8-cylinder engines.