OK I manage to 'solve' issue by connecting PS to an ACC 12V. I used the spare connector behind the HU
http://ae64.com/Rear-camera-16p-operation.htm
Used a multimeter to ID the ACC 12V.
Not ideal cos the cam will be on as long as the ACC is on.
Next step will be looking for a good cam works with 6V or buy an after market HU with 12V supply.