Tha Boss

Have an 88 GT and my headlights dnt come on wen i hit the switch. My parks lights come on but not my headlights. I thought it was my switch so i bought a new switch. Same thing. Parking lights run fine but headlights will not come on. I kno the headlights are working because i ran them straight off the battery and they workd. I need any help i can get or at least a wiring diagram for the headlights please
Thanks guys!!