What are the two black boxes in the house fuse box Aug 16, 2007Best Answer: The black boxes most likely are knife fuse holders that hold cartridge type fuses that act as the main breakers in a modern fuse box. Pull them out and the whole house will go black. I doubt if they have any bearing on your brown out. More likely, that Status: OpenAnswers: 5 Amazon: Fuse Boxes - Fuses & Accessories: Automotive 12-Way Fuse Block W/Negative Bus – JOYHO ATC/ATO Fuse Box With Ground, LED Light Indication & Protection Cover, Bolt Connect Terminals, 70 pcs Stick Label, For Car Boat Marine Auto Car Truck. by JOYHO. $17 $ 17. 95. FREE Shipping on eligible orders. 4.5 out of 5 stars 170.