How do you tell if an automotive fuse is blown under the hood?

You tell if an automotive fuse is blown under the hood by visually inspecting the small window in the fuse. A blown fuse will have a clearly visible broken filament (a thin wire inside) or a darkened area inside that window. Sometimes the filament is completely gone, other times just a portion is broken, causing the dark spot. If the window is clear and shows a continuous, unbroken filament, the fuse is likely fine.