Hi Jacopo,
Before I ask for the photos of your new car the issue does sound like it could be a fuse.
I'm not sure how the +4 is wired but can you see if anything else is connected to the indicator fuse. If so and its now working your problem maybe solved.
I'm sure one of the other guys with more knowledge of the +4 will help you in locating the fuses.
Now where are the photographs.
