PN 558-420 contains 5 extra input/output wires that the base Terminator EFI harness does not contain. It contains Input wires for Inputs 1-4. It contains one wire for Output 2. These inputs and outputs can perform features and functions that must be programmed via Holley EFI laptop software. The software also contains instructions on how to program these.
558-420 Terminator EFI Input/Output Kit