Dash lights come on when key is in the on position, but once engine is started and key returns to the on position only the exterior lights.

Could be the dimming function has failed. They tend to get hot and the resistor fails and the dimming signal to the panel stops. The switch is easy to replace, basically you remove the lower knee bolster panel (cover under steering wheel) then open the ash tray, you will see two screws in the trim, remove them, gently but firmly pull around the center trim to release it. Now gently work around the instrument cluster trim panel to pop the clips free, pull the switch out of the clips, disconnect it, plug in the new switch, push the switch back into the clips, reinstall the trim pieces and you are done.