An important consideration is the fact that I connected the box without connecting the box to the caravan (therefore no LED lights in the circuit), I got the sensor response based on the circumstances at start up.
If the box was attached at start up then the sensors were disabled until the vehicle was restarted (without the box plugged in)
If the box wasn't attached at start up I got sensors going off, regardless of the circumstances (again, until I restarted the car)
If its not related to the system-check recognising that there is "something" attached, then I can't imagine what it could be.
Do you have an alternative explanation?