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You're in the wrong forum. This is the X150 Forum, for 2007-up XK/XKR models. You should repost in the X100 Forum, which covers your 2001 XK8. Hopefully, a Moderator will move this thread.
If I remember my XK8 days correctly (no promises), the NAV box would have been in the boot, right-side wall right about where that white harness is hanging.