Disconnected wire near collant tank
 

so I was putting in my D585's when I noticed that there was a loose wire. Pic is attached - it's the red wire. What is this connector for?

What would be the best way of fixing this?

https://cimg4.ibsrv.net/gimg/www.rx8...bd654da843.jpg

also any tips on how I could clean my engine bay? Lots of old rustproofing oil on it...

Air conditiong pressure switch.

thanks, this isn't essential right?

It is essential to your AC system.

The best way to fix would be to disconnect the connector, pull the old pin out, crimp a new pin on the wire, slide it back in to the connector, and reconnect. You may be able to solder the wire to the old connector, although I cannot recommend trying that. If you could find the same connector online or at a junkyard or something you could cut it and solder it on to your wires.

that's the plan today.
I don't think that connector's pin is pullable.