You can buy a Plug-n-Play LS swap wiring harness or you can make a DIY LS swap harness. Pat walks through what Plug-n-Play harnesses do that makes them so popular. For one, every wire is clearly labeled to show where each plug & injector goes. Additionally, each of our wiring harness kits include detailed instructions and clearly labeled fuses. You can save a LOT of time going with a labeled, pre-made wiring harness.

Speedway GM Engine Wiring Harness, 1999-02 LS1
(91099021)
http://bit.ly/2ekEXIu

Speedway 2004-2008 Vortec V8 Wiring Harness, Extended
(91004084)
http://bit.ly/2eDexgj