The Switch will supply then remove ground to 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