Looks like its had an alarm fitted then hacked out, thats deffo not factory fitment. That wire isnt for the sensor its probably for the indicators or something, the oil temp wire will be buried behind the fusebox

The black wire is a spare ign live, the white blue is spare lights on feed and the brown wire will be an earth, if you cant see any other brown wires with no home to go to then its again a spare. VW had a std loom, and the spare connectors are used for options that were available at the time but not installed

Not sure what the red/black is, could be for an alarm follow it and see where it goes
