Update 6
As promised and also the main reason why I have yet to updated my build in a few months is I have been wiring and documenting the wiring on my 818. My goal was to wire up and get the car to run before I updated anything else. I am running a JDM 2002 STI EJ207 Engine and ECU with a 2003 USDM WRX harness. I deleted a lot of things and made a stand alone harness. My cars ODB2 port and OEM ECU work correct, and all the engine sensors are happy.
Note: I am running an Infinity Box so I am only running the engine with OEM wires. Lights, gauges, OEM fuses, and the OEM Relays are all deleted. You may need to keep a few more wire, relays, and fuses if you plan to not use an infinity box. This guide should still help. The main thing you will need if you’re not going to use an infinity box is the main relay, both fuse boxes (or make a smaller one), and the ignition relay. Again this is an engine only harness, if you follow this guide and don’t use an infinity box you will still need to wire your own body harness for things like lights, signals, wipers, horn, etc.
I have successful started the car and ran it with only a check engine lights for the rear O2 sensor and VSS sensor I had deleted.
Rather than reinvent the wheel with wiring diagrams I have edited the OEM diagrams and will explain each page as we go. The engine harness is all you need the rest of the lights, switches, and other optional things are all deleted. After you have gutted the harness you will only have engine plugs and sensors remaining. Goodbye OEM wiring: ABS, A/C, horn, cruise control, security, lighting, switches, relays, airbags, etc. Very light weight! yay! Here are a few pictures of it installed. And a video of the car running please excuse the messy garage! Video—> https://youtu.be/K3uzEFdS9VM
