harness integration question

[Ishmael]

I keep asking questions because I have no idea how certain things work. For instance with the stock engine wiring harness I have in the car, I just hooked everything up and plugged it into the factory style bulkhead. My ignition and everything else runs from there. With an ls harness, how does everything integrate? Am I splicing certain wires and retaining the starter wires? Is there a company that makes a retro fit engine harness that will plug into my bulkhead without any splices? I've got a ato fuse block from year one coming some day, it would be nice to be able to use it. I have to figure all this out before I jump on board.