I have the same problem it seems with my 2001 Focus SE Wagon. You turn the headlight switch on and the interior dash lights come on. They will intermittently go out sometimes while driving or even sitting in a parking lot. In order to get the interior lights back on, it sometimes works to shut the headlights off, then turn them back on. Sometimes they come on for a second then go dark again. I have tried to rotate the dimmer switch and leave it in a different position from normal, to see if that helped, however the problem still occurs. Des anyone know what is the problem causing this?Give the dimmer wheel a wiggle and try it at a different position than you normally leave it at.
The power source for the backlights in instrument cluster, HVAC panel in dash, and radio is the dimmer circuit inside the main headlight switch. This circuit uses an electronic voltage divider which in your case probably has an intermittent component as this device dissipates a bit of heat - especially when the dimmer is turned down. The simplest solution is to replace the headlamp switch - it is very easy to access. If you are on a budget you could consider a used switch but keep in mind that although all 00-04 Focus headlight switches are interchangeable there are two types: with or without fog lights so if your car has fog lights you want to be certain to get that type switch.The overhead lights work as they are supposed to. The Instrument cluster and panel illumination lights are the problem.
Thank you, Paul for clarifying.