Shot in the dark but maybe it goes to the G611/Radiator Identification Sensor plug? Only present on CBFA cars. Seems too short but I don't know off the top of my head how that sensor lead is routed.
If you can't figure it out you're probably better off sticking the engine in and then pulling codes after starting. That should point you in the right direction.
EDIT: Took a look under the hood of my car and that part of the harness is difficult to see under the intake manifold. However, it looks like that wire is routed straight down towards the ground. Short of jacking up the car or pulling the throttle body pipe off I can't get a better look (sorry, I'm at work so not gonna do that
).
