This modular kit is perfect for the budget minded or the build it as you go crowd. It lets you completely customize your harness to suit your vehicles needs. You start with the Basic Circuit Kit, a pre-wired 4-circuit fuse block with two mounting trusses. As your project grows, you can add additional circuits, using the pre-wired 4-cicuit add-on fuse blocks listed below. The fuse blocks and trusses interlock for a professional looking installation.