Headlight switch - 75 Duster - Stumped...

Notice the "P" (parking) is not used. Ma hooked the parking lights to the tail light circuit to keep them on. Yellow is the ground for the dome light AKA "twist the knob" to the left

Tan is the output of your dash lamp dimmer

Green is the headlight output going to the dimmer

You already know B1 is main power to headlamps, B2 is "the rest"