leave the original loom in place, plug everthing in that you need on the turbo loom and separate it from the rest of the car loom, lights etc.
if you chop the turbo management loom from the main loom where the wires end at the fuse box, fuel pump relay & clocks you will have 5 wires to connect, 3 switched lives, 1 to the fuel pump relay & 1 to the rev counter.
to tidy things up what ever is left of the 3i loom that will not be used u can can then strip this out in the same way.