The Mallory 628 Window RPM Switch is an RPM switch that is triggered from the tach terminal available on most aftermarket performance ignitions. It will not only activate at a particular RPM, but can also be set to de-activate at a second, higher, RPM. It can be used on 4, 6 (even-fire only), and 8 cylinder engines. NOTE: The Mallory 628 CANNOT be triggered from points or electronic distributor. It must be triggered from a tach output terminal. The 628 features two independent sets of switch contacts that switch other devices on or off when the selected RPM is reached. These contacts draw a maximum current of 5 amps. To switch more than 5 amps, you must use the RPM Activated Switch output to drive a high current relay, such as a horn or headlight (see illustrations). NOTE: The switch contacts are NOT connected electrically. This allows you to turn one circuit on and another off at the same RPM.