Ignition controlled power supply for caravans - pin 10

[Simon J]

I recently fitted a Volvo trailer module and towbar cable harness to my 2005 V50 and find to my surprise that the ignition controlled power supply to pin 10 (often referred to as the 'fridge circuit') is live as soon as the ignition is switched on and not just once the engine is running. This seems very odd to me but the Volvo description of the connection, even on the latest XC40 and V60, is simply 'Battery voltage - ignition on' so it seems to be standard Volvo practice. It's actually referred to as 'Battery charging' in the instructions for fitting the wiring to the V50 which seems even odder!

The effect of this would be that the fridge (if present and connected to the tow vehicle) would be drawing current from the car battery as soon as the ignition is switched on and thus while the engine was being started, which doesn't seem like a good idea; and secondly the battery charging circuit - pin 9 - would be connected to the caravan battery by virtue of the habitation relay in the caravan being triggered by the fridge circuit, and thus starting the engine would draw current from the caravan battery on wires intended simply to charge it, which also doesn't seem like a good idea.

I had thought that perhaps the power to pin 10 might have been cut while starting the engine in the same way as it is to the radio, but seemingly not.

In reading through the threads I noted that on some cars, pin 10 isn't live until a fridge is connected to it (although how that would affect the operation of the habitation relay if a fridge isn't fitted isn't clear) but in my case pin 10 is live as soon as the ignition is switched on.

Can anyone throw any light on whether this is how it's intended to operate as it seems to me to be a flawed arrangement.