2000 Pontiac Grand Am no lights

Do the rear turn and brake lites work ok? Might be an issue with the multifunction switch? Do you have voltage at the park lamp fuse, use a voltage tester. If the fuse is good, that is great, but, you still need to check for voltage. If no voltage the circuit is dead.

The orange wire at the headlamp switch should be hot/voltage all the time. When you turn on the headlamp switch, the brown wire becomes hot/voltage and carries voltage to the tail lamps. It could be a faulty wiring circuit somewhere? I always start with basic testing.