Headlamp & Horn

Okay, I'm taking the lazy route for a second and asking here.
Wiring diagrams give me a headache.
75 Dart SE, turn the headlamps on and no horn.
Turn them off, horn works great.
Does the horn go thru the headlamp switch and if so why?

I rarely drive the car, and when I do, seldom at night. Drove it the other night and of course Bambi want to walk out in front of me and when I laid down on the horn, nothing.