According to http://x3.xbimmers.com/forums/showthread.php?t=530507
The X3 has (2) fuse blocks:
Fuse Block #1 is behind the glove box and is accessed through the removable panel at the far right at the back of the open glove box. The fuses are (5) or (6) inches behind the back of the glove box and will probably take someone with a very thin wrist or better yet, a surgical forceps or very long nose pliers to change. This fuse block houses fuses Nos. 1 through No. 67.
Fuse Block No. 2 is housed in the right rear fender. To access it you must remove the small right rear storage cover (pull firmly on the black hand hold). Then you must remove the plastic "push rivet" at the rear of the insulation cover. Pry the center pin out with a screwdriver or small knife, and then completely remove the plastic "rivet". Then simply roll the insulation cover forward and you will find the fuse block.
Fuse block No. 2 houses fuses Nos. 100 to No. 204.
The sheet listing the fuse locations for BOTH fuse blocks is folded and stored in a slot at the bottom of the fuse block (No. 2).
Or: Try watching this YouTube video: https://www.youtube.com/watch?v=-Ph-KB7LIu0
if I helped you, please let me know. :)