The Multi Map Selector is designed specifically for use with Holley Dominator EFI systems (not HP). It allows for up to four different calibrations (Global Folders) to be selected at vehicle key-on (startup). The switch is connected into the J3 ECU Connector (included). Multiple maps can be used for many different purposes, such as different fuel types or octane, maps for different track conditions, different nitrous setups, etc.