Mine's routed to my ashtray, along with a switched micro USB power supply that I ran from the fuses in the glove box to the ashtray, still without doing anything except pulling the heater controls. You can get a hand up there really easy. No need to remove vents.

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2005 E53 4.4i
2003 E53 3.0d (Mrs)
95 E38 740iL (sold)
93 E32 735i (sold)
91 E32 735iL (sold)
93 E34 535i (sold)
89 E34 525i with M30B35 conversion (sold)