Jaguar Fiber Optic Loop DE35JAG005 X350 x150 x200(?)
 

Fiber optic Loop for S-Type, XJ, XK, any of the cars with the fiber-optic Alpine Stereo need this Loop in order to install the Jaguar audio control module or other accessories. If you're reading this you probably already know what it is. I'm not sure about compatibility, may work on other models.