One of the pins in the SCART lead is wired for the changeover signal
So when you turn the cable box on, it will flip the TV to its AV channel, then when you turn the DVD player on it's effectively changing the cable/Sky box to its own AV input channel, which it then outputs to the TV.

Some boxes/DVD players don't output the signal but this is pretty rare, most TVs should receive it. If the channel isn't changing over automatically then the problem is most likely the lead not having the right pins wired, as I stated above.

Thinking about it now I'm more awake though, I'm not sure an American DVD player will have SCART. Composite video is more common over there I think.
(Son of Sam-i-am We're all as mad as hatters here, Wed 7 Jan 2009, 9:23, Reply)