Three lever light switch:
If top lever is straight up and down= everything off
If top lever is in stop light you get brake and turn signal lights
If top lever is in service drive you get brake lights, turn signals, parking/running lights and headlights
PROVIDED lower left lever is not in park, then headlights are off but every thing else is on
If lower left lever is in any other position, [top lever in service drive] headlights should be on
That said, most trucks parking/running lights IN FRONT turn off when headlights are on [easily changed]
Lower left lever controls brightness of dash lights save for the park position which turns off headlights and gives you dim dashlights