Testing caravan breakaway switch - no response

Pulling the pin from my Tekonsha 2010 breakaway switch while the caravan is parked up and disconnected from the tow vehicle seems to do absolutely nothing (i.e. no brake lights come on; no noise at the wheels indicating magnets engaged and pads attaching to the drum).

I understand removing the pin should immediately apply the caravan brakes for up to 15 minutes, or until the pin is re-inserted. However, I also understand that there needs to be a power supply to activate the device, but I have never found a dedicated battery for the Tekonsha in the caravan. Another option appears to be a connection to the caravan 'house' batteries, but this seems unlikely because they are always kept up to full charge by roof top solar panels, yet the Tekonsha is not doing what it is supposed to do.

Logically, the only alternative is that the device has its own in-built power source which is only charged/activated when the caravan is connected to the tow vehicle's electrical system. Unless there is a fault with the device itself or its wiring connections, then I assume the latter must be the case. I am yet to re-connect to the tow vehicle to put this to the test, but if other members can suggest an alternative course of action I would welcome their input.