Which pin tells an iPod dock that it is connected to an iPod?

[Xebozone]

I am making a iPod Dock (Female) to 3.5mm and USB Power cable for all MP3 players.
I have stripped down a dock extension cable, and labeled each of the wires according to the pinout located here
http://pinouts.ru/PortableDevices/ipod_pinout.shtml

I have confirmed my labels correct by powering on a USB fan through the cable using a direct power source (A mains->USB adaptor).

The problem I have now, is that my dock itself will not output power to the cable unless it thinks an iPod is connected to it.

What pins do I need to modify so that it realizes that a cable is connected to the dock?

[Jeroen3]

21, read description