I have a MESS of wires coming from a grommet in my firewall and also a connecting block with 4 connectors near my brake booster. I have a modest understanding of car wiring is there some sort of picture diagram showing how all of the various harnesses (ie engine, headlights, marker lights) connect to the car and where they run? I'm trying to decide whether or not to sort though this jumble of crap or to disconnect them all and start with new wiring.

There are diagrams in the factory assembly manuals and other places that you can purchase wiring diagrams.

If you are doing a reconstruction, I would suggest replacing the harness. 32 year old wiring can and will eventually short.