ok I am a bit wiser now
On newer caravans and I don't know when newer starts from but pin 9 "should" be permanent live. There should be a relay in the caravan that is powered by pin 10 which should be ignition live. When the engine runs this relay connects pin 9 to the leisure battery and disconnects the caravans 12v system, not road lights. The leisure battery is then being charged.
With the engine off pin 10 loses the live and the relay disconnects the car in 9 from the leisure battery and reconnects the caravans 12v system to the leisure battery.
Apart from the ATC I still don't think I can see the point of pin 9 being permanent live. I now need to see if my caravan has the relay I have referred to. Odd name, it is called a habitation relay. If not or it has failed that could be why the car battery went flat when the caravan was left connected overnight.
macafee2
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