Yeah , it's usually nr 54.
I had a shortcut, well my wife had one :-) she usually puts the keys in the cupholder, and there was no plug in the 12v outlet, probably a key that shortcutted the circuit..... ???
I think it blows when keys on the keychain together with the carkey are put in the storage compartment in the middle front shortcuts the front outlet ..
Here's my thread on the matter earlier..:
http://x3.xbimmers.com/forums/showthread.php?t=633500