**sorry for the off topic rally wagon**
I can't remember all the details exactly but when I did the swap I did the following:
I brought ALL the EJ20G engine wiring in through the AC hole in the firewall. This is the engine harness and the boost control, ignitor wiring etc. wiring all in one wrap. I then connected the ECU plugs to the appropriate wires on this wrap. This is easy if you have the diagram. BUT you can't take any short cuts as it is important to separate the power and signal grounds as originally intended.
At this point I had BOTH sents of engine wiring in the car. It's not really that much wire really. Remember that most of the wiring is on the "engine" harness. I just supplied the to-the-engine-plug wiring.
To switch to the turbo setup I dropped in the engine, attached the connectors and then delt with the ecu.
The only remaining wires were something like: kain power, switched power, speed sensor input, tack output, diagnostic switches (I used these), check engine light and the fan relay. Maybe one or two more. I am convinced that if I did it right I could have left the old ECU connectors and had a completely swappable setup. NA to turbo to NA without much difficulty. However, I did end up cutting everything away.