Pin 10 offers power to whatever is connected to it on the trailer/caravan. It is, I suspect, irrelevant to the car what is attached to either pin 9 or pin 10, provided the load isn't excessive. There's a 40 amp fuse for the trailer module which presumably covers both pins.
The issue to my mind is simply why does Volvo not delay providing power to pin 10 until the engine is running, something that would surely be simple to include in the trailer module software?
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Simon J
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