I have decided to clean up my wiring and run everything (except subwoofer) through a DIY Dbox before installing LED reverse lights. For anyone unfamiliar with the Dbox here is a link to the youtube video.
It seems like a great way to safely reduce clutter and make installation and removal of auxiliary components a lot easier. Unfortunately I am having some difficulty determining the gauge size of wire required, as well as the correct fuse. The reverse lights I am going with are a low cost pair of 18w on amazon. So 18+18/12 = 3 amps, go to the graph for wire gauge selection and 18 will suffice, 15amp fuse between the battery and relay will make the fuse the weak point. So does this 15 mean that there is essentially 12 amps of safety between the aux draw and having an issue? This is where my trouble begins.
If I have 2 circuits going to this fuse box that pull 220W respectively, one pulling 36, and another pulling 500 for a total of 976W that works out to around 85amps to be safe. So the wire with the inline from the box to the battery should be 12gauge and my fuse should be 80? I have never heard of anybody using an 80 amp fuse and it seems excessive but the math seems to workout, unless of course I am missing something.
Since that one load is so large I will also need the wiring within that circuit to be 16gauge in a few different places as well, from the fusebox to the copper crimp where all of the circuits come together, from the output of the fuse box to the relay, from the relay to all its connections, and from the switch to its ground right? This circuit would also require a 40 amp fuse in the fuse box if I'm not mistaken. If there is something that I have overlooked or if the calculations I am using are incorrect please let me know. If it helps I can try to work out a diagram of how I am understanding this device to work as well as what the size of each component should be and explain why. Thanks for any input.