Jimny tail lights not working

some (new) cars got a small switch inside the trailer socket that switch off the lights when the trailer lights are supposed to do the job. Haven't seen this on a jimny though. when there is a adapter from 7 to 13 pin connection in the socket the lights might be disabled.
(not sure if you got the two types of trailer sockets in UK)
Had to fix a switch like this on a VW Amarok once..

Anyways on my car the trailer wiring loom is plug and play into the original sockets inside the car out of the weather.