Likely your MY2004 is different than my MY2000 but perhaps it is somewhat similar. Per the factory wiring diagram for MY 2000, antenna amplifier power comes from a white wire that is on pin 5 of the black connector on the back of the stock radio head unit. This is referred to a "Plug A" and should correspond to the diagram on the back of the radio.

The attachment is partially from that diagram and partially from a Becker document.

Hope this helps.

Lynn