Please excuse the story leading up to the question. (or just skip to bottom)I've had the car almost 3 years now and I recently rediscovered something that kind of gave me pause when I first bought the car. When I found the car listed I immediately fell in love. Called to schedule a drive that day. The drive was great, no noticeable issues, sounded amazing, all the little things worked. But me being the "there is always a catch" kinda guy I gave the car a good visual inspection, and upon opening the hood I immediately noticed a broken wire in the area right next to the oil filter housing, well, on it specifically. (this is on a 35si) The dealership was great and immediately took it to the shop to fix the wire, while they verified with my bank. They brought the car back from the shop and I checked it again and they fixed the wire in question. At this point I was excited and anxious for many reasons, (it was a rough week anyway, and was in a big city, got lost on the way to the dealership, not looking forward to drive home) so didn't look THAT close as to what the wire went to. Been happy with the car all this time, no issues other than dead battery that was original with the car back in 2011.
Now flash forward three years. My brother-in-law pasted away last year, and has always done my oil change for me. (I've always been panicky under a car, but with the Z4 more so, as it sits so low.) Anyway, I found a set of ramps that the Z4 can actually drive up and that I feel comfortable to get under, I hate jacks. Well, when I got to the oil filter I noticed and remembered the wire. Curious I looked a little closer to see where and what it goes to. It appears to go to some sensor, possibly oil pressure? Now what puzzles me is that almost every sensor I have ever seen has at least two wire leads to it, possibly more. Upon closer inspection the back of the connector looks to have had the spot for two wires, but there is no evidence there was ever a second wire that had broken off, nor did I find any broken wire further back in the engine bay. And even more strangely thinking back on it, if it was indeed oil related there was never a check engine or oil light during my 30min+ test drive when I first bought the car, so it must not be critically important.
Does anyone know what specifically this is for? Is it / has always been a single wire? Is it grounded through the engine some how?
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Someone get me a shovel. 
