Method and device for detecting the presence and type of trailer which may have been connected to a vehicle including arrangements for applying a first voltage to a first amount of power lines for a first sub system in the trailer and arrangements for measuring the individual currents consumed by components in the first sub system. An arrangement is also included for comparing the individual currents to a first predefined threshold. The device additionally has arrangements for applying a second voltage to a second amount of power lines in the first sub system in the trailer and an arrangement for measuring the total current in the second amount of power lines, together with an arrangement for comparing the total current in the second amount of power lines to a second threshold. An arrangement for making decisions is provided and adapted to decide which kind of trailer, if any, is connected to the towing vehicle based on the measured currents.