mine will blow that fuse spontaneously as well, but only like every couple of months or so. I dont know what causes it either, but it sure is frusterating, especially with people in the car!
Ryan

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83 300SD.......sold
96 integra SE....sold
99 a4 quattro....sold
2001 IS300.......sold
2002 330i.........current.
2004 highlander limited....current.