Traditionally, Mercedes-Benz has taken the entirely logical step of printing a legend of the fuses and what circuits they relate to on the inside of the fuse box cover. By referencing this, you can quickly identify what each fuse does while you’re in there checking whether they’re blown or not. For some reason, however, sometimes Mercedes placed a paper diagram of the fuse layout in the boot with the jack and tools. So check there as well. The owner’s manual should also offer this information in the electrical section. If none of that works, you can Google the make and model and ask for fuse box information. Don’t forget, either, that there are often two fuse boxes in many modern cars; one under the bonnet and one under the dashboard or inside the glovebox.