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 laptop software. The software also contains instructions on how to program these.

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Installation Sheet
Holley Terminator EFI Input/Output Harness