Wiring Harness Information - LT1 Swap 2004 Pontiac GTO Wiring Harness Info - Wiring harness info specific to the 2004 GTO LS1. wwwarness - Adam will rework most LS1, Vortec Truck, and F-Body LT1 Harnesses. wwwodharness - Purchase new harnesses for swaps, Vortec 4.3, 5.7, 7.4, LS, LT2007-2009 Vortec Harness · Vortec 8 Info · GM ECM Tuning 94-97 LT1 / LT4 Stand Alone Engine Harness - CPW | LSX Built From Scratch Stand Alone Engine Harness. An engine management harness is pretty much what you will find from most wiring harness companies. Basically, it contains all of the necessary functions to make the engine start and run, while also supplying any necessary signals from the computer such as speedometer and tachometer.