1984 Chevy Blazer truck will not start

I have a 1984 k5 blazer that will not start. I have no interior light, brake lights, etc. I only have headlights. And worst of all my truck does nothing when the key is turned, I can't even get it to a mechanic. The battery is good as is the wires, I replaced the fusible links, but I still have nothing except headlights, and i'm lost. I feel like i've checked and rechecked but to no avail. Please help with my truck walkin isn;t cuttin it.