No taillights, brake lights, hazards or dash lights

I'm not familiar specifically. But somewhere there has to be a connector separating the rear harness, and you can probe that. It is likely near same area as A bodies, IE somewhere up in left kick panel area. That harness MAY go down and back at the engine bay firewall

Make sure fuses have power on both sides. Probe the hazard flasher as it should have power TO it at all times. If it shows power, turn on hazards and see if power goes away. If so, suspect bad fuse clips or some sort of bad connection for the feed into the fuse panel, etc

Brake lights--same deal......Brake switch should have power at all times

FUSES. Check them for power UNDER LOAD on both ends at the fuse clips. It is common for fuses to sometimes blow or fail "back in the cap" where you cannot see the break. Something that old ALWAYS suspect corroded/ loose fuse clips