Congrats on the 65! That piece on your x is ultimately useless. It goes to your trunk- my jag tech here just calls them poppers. They pop up your trunk from to closed position when you hit the trunk realease button on key fob. they are supposed to be located next to the trunk arm brackets in the trunk rail. Look on both sides, you may have one still intact. Im pretty sure this is what that item is. I worked for my jag dealer when I was younger as a lot kid, then a sales assistant... then I left because I didn't want to become a life-er... Hope this helps!

 

These are not the poppers, as I changed them last year as one was broken. This piece is located on top of the wheel well. As some same it is probably a mount for a lock for your tires.