Tow Bar Wiring Relay Question

[cma]

Had my tow bar fitted by Audi as I needed the fan upgrade (the wallet is still crying)

Was just checking they had wired in pin 9 and 10 for the fridge and perm 12v feeds. Fridge wiring was fine when checked but the permenant 12v was not there.

Further investigations traced the wire back to a relay. Once the relay was activated then the pin became live as it should do. but I couldn't trace down the activation wires without stripping the boot area apart.

So my question is What is the relay for and what causes it to get activated?

[c.grex]

My understanding of the Permanent 12v is that it is used for charging the Battery on the caravan. If it was live all the time, when you stopped for a break it would drain your car battery. The relay usually looks for a voltage of over 14v, as this is the voltage you should get when the car engine is running.