1998 Chevy Tahoe Headlights/Instrument Panel

With the vehicle is running and light switch is off; the drls are on, drl indicator lamp on; when the light switch is turned to parking lights; the drls are on, indicator lamp on, parking lights on; nwo the PROBLEM - when the switch is turned to headlights; the headlights turn off, instrument panel lights go off. Can't figure out problem; not bulb; not fuse, not under hood stuff.

Thanks!