I have an OEM BMW analogue tuner in my E46. The cable that fits between the TV tuner and the NAV module lets me add aux video. I can see this as a choice on my TV HU display. I use the "second" video input using the backup camera lead on the loom for my CarPC. So the OEM BMW tuner gives you the choice of two Video Inputs. The loom I purchased has two video inputs, audio input and brake light switch (to ground). I guess this is a modified from standard loom though.

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E83 - Aero PKG Mods installed: Homelink mirror. CIS-IBUS video module, AUX, Rr Dr Release, stock wheels, Remote start, CarPC (Atom) & mud flaps - NAV - MKIV - NA Map DVD - 2011
E46 - 18.5 wheels/tires (summer), 17 stock (winter), Homelink, NAV software upgrade, BMW video module, Radio to V53, AUX, USB IBUS interface,BMW alarm install, CarPC(Epia), remote starter, tank battery & angel eyes. NAV - MKIII - NA Map CD - High Version 2008.1