I found a fuse under the glove-compartment, that was blown, so now the lights on the car works again. But i still need to find out why it lights up the brake lights, instead of the normal lights on the trailers ;-/ It looks like the trailer socket is connected correct (wiring).

Hi LZ. I just got a used Disco 4 2011. Had it for at week but to day when i pluged in a trailer, first the brake lights were constant on, on the trailer and the left side tail lights whent out, they stayed turned off until we turned off the car, removed the trailer cord and turned the car back...