question about plug from alternator wire sr20

[Volchok]

I have a rather simple question:

I just pulled out my sr, my first, and labeled petty much all of the wiring to be safe during the install. When I put the motor back in an began to reconnect everything, I ended up with one plug i was unfamiliar with. I didn't label it and don't remember unplugging it. I know I need to take a picture, which i should have laready but it was alte and dark alst night and I didn't get a chance to take the pic. I will if no one knows what it is from its description.

It is a single yellow wire coming off of the same lead as the alternator wires. It has a plug on the end with a rubber cap, simialr to what connects to the negative terminal on the starter. All three connectors are on thwe alternator, this one is really greasy and dirty and I have a feeling it was just unsed, but I need some opinions from people who know.

thanks in advance zilvians.

here is how it looks as of now:
before:
http://www.teahnshawn.com/gallery/albums/upload/240SX/normal_PICT3091.JPG

After:
http://www.teahnshawn.com/gallery/albums/upload/240SX/New3/normal_PICT3437.JPG

[onepuff]

Sounds like maybe the oil pressure sensor.

[Volchok]

oh man i think you are right!!!! Thanks!! I forgot about that, as I am now using a Defi Oil Pressure gauge, and blocked the original port so I could get the oil cooler sandwich plate on.

Thanks a bunch, really.