Wow, thanks for the original posters of this thread! Exactly what I've been searching for with no avail, you have no idea the weird input into the google search engine which makes this thread pop up. I can also confirm all of this works, and will be looking for put the relay into my circuit, as I can hear a constant ticking when the tel in is wired premanently to 12v switched supply.
Just to add an extra I am using the dension kit to simulate a cd changer and usingthe inputs there.
Cheers for this!