E30 Fuse Box Diagram, High Resolution, Printable | E30 Gruppe The fuse box is where you want to start with many problems you may encounter with your E30. While relays rarely go bad, it’s still very possible. One thing you can always do to test a relay easily is if your Horn is working, put that relay from K2 into the Low Beam K4, or other slot which you’re trying to get working. Download the E30 fuseAuthor: Tone Fuse and relay box diagram BMW E90 - fusesdiagram Fuse and relay box diagram BMW 3 E90. Identifying and legend fuse box.