This harness is designed for the 1999-2006 4.8L, 5.3L, 6.0L mechanical throttle body engines using an LS1 / LS6 PCM with a 4L65E, 4L70E, 4L80E, or 4L85E transmission. 2003-2006 Engines will require a mechanical throttle body to be installed. 2003-2006 engines which were originally flex fuel will also require Delphi Multec 2 (factory truck style) injectors to be installed. Harnesses do not include connections for the rear O2 sensors or fuel tank pressure sensor but are available separate. Included with this harness is a 10 circuit weatherproof fuse block, detailed step-by-step manual, and GM color coded wires with labels for easy installation.