The headlights, power door locks, and horn do not work. All fuses are fine. All fusible links look OK. The interior lights, radio, radio memory, power windows, AC blower, speedometer/gauges, cigarette lighter, glovebox light, turn signals, reverse lights, brake lights all work.

Any idea what would cause the headlights, horn, and power door locks to not work?

I would double check those fusible links again. It sounds like one of them is not good.