The ISO standard doesn't preclude pin 10 only becoming live once the engine is running; it simply says that it's ignition controlled. My problem/concern is that with pin 10 being live as soon as the ignition is turned on then the fridge will be drawing current from the tow car battery at the same time as the tow car engine is being started - an unnecessary extra load on the car battery; and the habitation relay will activate the battery charging circuit on pin 9 which will mean that starting the tow car engine will also draw on the caravan battery across wires designed for charging, not starting.
Having pin 10 only going live once the engine is running avoids both of these situations.
I realise of course that a voltage sensing relay would solve this, but it seems odd that it's not done automatically.
__________________
Simon J
|