Hej Bjorn
Just grip the horn button assembly and pull towards you, it's just a push fit and held in place by a large rubber 'O' ring.
It may not be the button itself at fault, when you remove the button you often find the wire is unplugged from the terminal and is resting on the metal hub and randomly contacting causing the fault you describe.
Which part of Sweden are you in? I have many happy memories of southern Sweden as I spent one week a month in Gothenburg for many years (I worked for Volvo Cars).
