When I got a new ipod (4G nano), the dealer installed cable would no longer charge the ipod (I could control the unit fine). This is due to the change Apple made to the newer ipods/iphone. I got the Scosche passport ($25), and this solved the problem.

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2012 F10 550xi Carbon black/oyster
2011 E92 M3 SSII/black
2012 W166 ML63 Steel grey/porcelain
2007 E93 monaco blue/beige (retired)
2010 E70 35d Space grey/saddle brown (retired)