'97 Chevy Express 1500 conversion van, 5.7 VorTec, Auto trans, bought new.
Radio light and transmission gear indicator light work, and dim when turning on the headlights. Dimmer adjusts light on them, but the rest of the dashboard stays dark. All the fuses in the panel by left foot test good. Where else to look?

 

Seeing that it's all the lights, I'd suspect a loose connection somewhere.

 

Do you have power at the wire coming out of the headlight switch? There should be one that powers the dash lights....I'd have to check a wiring diagram to see.