Headlights and interior/dash lights will not come on, but engine starts

Have the trouble codes checked. We can check voltage and ground circuits at the headlamps, go from there. In the diagram, the wires on top are voltage wires for the headlamps, hi/lo beams. Black wire is ground.

The headlamp switch controls part of the ground circuits. The headlamp control knows when the headlamp switch is turned on because certain circuits are grounded.