How does the fuse box get power?

[greg64]

I had similar confusion with my fuse block (77). It sure look like there are two 12 gauge wires feeding the fuse block through the firewall. But on my truck, only one of those two wires actually powers anything. It feeds a bus inside the fuse block, which then feeds all the fuses. That then feeds the blower motor, radio, etc. The headlights are unfused at the fuse block.