Yeah, thanks cobber, but I clearly didn't explain myself fully.
The camera has no screen and needs to transmit the video signal to the head unit for the video to be seen.
Obviously it is currently connected for video by the usb. If I connect it via the USB on the head unit, I can see and review any video, unfortunately the usb port is currently occupied by a tyre pressure sensor system. I have a two wire 5volt supply already but I need to know how, or indeed if, I can get the video signal from the camera to the head unit using an rca phono type plug.
David