ATC random breaking

[Dustydog]

We had the Jeep done last year by a Nationwide specialist company, but stating we did not require the permanent feed for the fridge has raised concerns. We seldom connect up with the engine switched off .

I would normally reverse up with OH guiding me, then lower hitch onto towball. connect breakaway and lastly the electrics. ATC does its thing and green light is on.

The feed to the fridge is never permanently live for obvious reasons. It uses pin 10 which will only supply current with the engine running .

 

[RogerL]

....ATC is always wired by convention to the permanent 12 volt supply which is always present in a 12S socket and the more modern 13 pin socket.
This is why the ATC performs its set up test on connection.

The OP has narrowed the problem to the caravan as the problem has occurred with 2 different tow cars.
IMO .....I agree with others.
There is an intermittent wiring disconnection in the 12volt supply to the ATC.
I would look for a fitted connector under the front of the caravan and check it for electrical continuity.
These connectors are exposed to the elements.

Basic trailers don't need a permanent 12 supply so it isn't always wired for 12N, 12S or 13-pin.

 

[Buckman]

The feed to the fridge is never permanently live for obvious reasons. It uses pin 10 which will only supply current with the engine running .

When we crossed to France or Spain with previous Jeeps I always disconnected the electrics as did not want a flat battery on arrival at the port. I came across this article regarding the Sterling Wildside.

The Sterling BBC1225 'Wildside' battery-to-battery charger provides fast charging of your caravan or trailer battery via your vehicle's towing socket. It takes the low voltage at the towing socket and boosts it to provide the correct, multi-stage charging profile for your battery. This unit is particularly suited to those who prefer touring, and so don't have frequent access to campsites with mains hook-up, and/or those with vehicles whose engines are Euro 5/6 spec.

The traditional method of charging directly from the alternator via the towing socket offers very poor performance because of the small cable and long run lengths used. This results in large voltage drops meaning zero to little charging of the auxiliary battery takes place and often the on-board fridge simply can't operate at the low voltage provided. Electrical demands have increased in modern caravans (caravan movers etc.) meaning that good charging has become even more important, however, with the introduction of Euro 5/6 engine vehicles with 'smart' alternators, the charging performance has, in fact, become even worse. This is because these alternators reduce their output voltage to save fuel when the starter battery is nearly full, which amplifies the already poor situation with voltage drop and effectively renders the charging system completely redundant.

 

[Gafferbill]

Basic trailers don't need a permanent 12 supply so it isn't always wired for 12N, 12S or 13-pin.

.....nowhere did I mention 12N wiring which is irrelevant when trying to help the OP.
12S and 13 pin plugs have a wiring convention.
Since the OP has described his ATC going through the test procedure when he connects his caravan, I assumed his 2015 caravan has a 13 pin plug which is wired correctly.
Discussion about fitters carrying out incorrect wiring....12N wiring and fridge wiring are just "noises off" as far as I am concerned!