Thanks again Tom.
I wasn't able to find any. But I grabbed one of the lightbulbs and tried to light it up with different battery packs. In the end it needed around 4-5V. However, I tried using an adapter and of course, it was not enough to light up everything (max 12V). It has a lot of lights.
I checked a christmas tree I have, and it doesn't have any sort of conversion from ac to dc, so I decided to give it a try and plug the decoration directly to the current. It worked well, everything lit up, so I have to assume that the box really is just a package for the fuses. It really sucks, it's a block of thick plastic and I don't have the proper tools to just break it and peek inside, but I don't know what else it could be!