Alternator wiring: loose yellow wire?

[sck_nogas]

Background: I have a D4BF engine, so I have 2 types of alternator connections have been grafted to the existing wiring harness, plus the two thick wires that bolt to the alternator output. This weekend, whilst changing out the alternator, the copper crimp eyelet terminal broke. So, I needed to crimp on a new one. No biggie, but as I did I noticed an "extra" wire and have NO idea what this is for?

So, here's the wiring diagram.

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With the colors coded in Blue in the image, and the FOUR wires that connect to the alternator.​

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But, this is what I have in that wire bundle...

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I see five wires!!!​

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Blue, red/white, 2 thick white and some weird yellowish white with a female spade connector?​

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And the after picture with my new crimp eyelet terminal (and alternator boot) installed.​

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Any guesses as to where and WTF this wire is for?

 

[Growlerbearnz]

Yellow is the oil pressure sender. I guess they bundled it into the alternator loom because it's in the right area.

And please, for the sake of my OCD, could you hit that black 2-pin connector with some deoxit/contact cleaner and dielectric grease? Ewww.