The Edelbrock IgnitionIAC Harness 35713 is a supplemental kit designed specifically for those who have purchased or are planning to purchase a Pro - Flo 4 EFI System for the Chevrolet Gen III 24X LS engine with either the 4150 - style or Pro - Flo XT intake manifold. The 35713 Harness Kit is required and must be ordered separately due to the two different crank trigger designs of the Gen III (24X reluctor) and Gen IV (58X reluctor) LS engines. The Gen III 24X LS engine is easily identified by the crank sensor located at the rear of the block behind the starter, and the camshaft sensor located at the rear of the block on top. The Edelbrock IgnitionIAC Harness 35713 connects to the Pro - Flo 4 LS EFI Kit's main harness labeled CoilsIAC and provides connections for the Coil Pack harness, Crank Sensor, Cam Sensor, and Stepper IAC Motor. This harness is a supplemental kit that is required when installing a Pro - Flo 4 LS EFI Kit on a Chevy Gen III 24X LS engine. Edelbrock sells the Gen III 35713 and Gen IV 35714 harnesses separately from the Gen III and Gen IV Pro - Flo 4 EFI Systems in an effort to keep production costs of the two LS EFI LS kits to a minimum and prevent the waste of an unused harness in each kit. Detailed instructions are included with this kit, and technical support is available in real - time chat on the Edelbrock website or you can call the Tech Line at (800) 416 - 8628. (Note Owners of the Gen IV 58X LS engine that plan to install a Pro - Flo 4 LS EFI Kit must order EFI Harness 35714.)