Holley Hemi Main Harness 558-115 | Gen III HEMI Harness with TPS and Idle Air Control Connections. This wiring harness interfaces a Holley EFI ECU to a Gen III HEMI engine with an aftermarket cable actuated throttle body. It is meant to be used in conjunction with an injector harness, a coil harness, and two ignition modules. Most stock sensors are used with this harness. There are two optional connectors for interfacing with CAN-based Holley modules.