Hi, The caravelle / transporter uses can bus so finding on it is a real pain. I have just found a acc line for my rosen dvd system i have just fitted to my 08 caravelle. You can pick up a acc ( switched live on ignition ) from the rear of the lighting switch. You can get to it by gently prising off the side panel from the edge nearest the front drivers seat. You can then use the live and ground by the radio if you require as normal.
If you are fitting a handsfree kit don't bother with a "mute kit" by far the best way is to chop the speaker lead and wire it onto the "phone" plus on the back of the radio. I didn't have a plug so I had to carefully solder onto the pin ( i think they are 6 and 12, they are the only two pins on this plug) Then take the mute wire to the radio mute pin on the back of the radio. This works very well.
I hope this helps!