Originally Posted by 2slofouru
I found it easier to leave my ej18 harness in the car and splice the ej20k ecu plugs in and add the boost solenoid harness. Also swapped the maf sensor plug and extended a couple of other engine harness wires. Doesn't look stock if you look closely enough but the people I've shown can't tell. Didn't have to remove the dash or any of the rest of the harness.
The 95 EJ18 ECU harness comes out with two plugs behind the dash. It's separate from the complete bulkhead harness. You don't have to pull the whole bulkhead out. You unplug those two plugs, the ecu plugs and the plugs at the back of the engine and pull the whole ecu harness out. Merge about 20 wires, separate the jdm ecu wires into 3 branches, one to the solenoids, one to the back of the engine and one to the 2 plugs on the side of the engine. Run everything out the original firewall hole the ecu wiring passed, it all fits, then in the engine bay over to where it goes. This can all be done in just a few hours.