Two problems related to fog light switch have been reported for the 2003 BMW 330. The most recently reported issues are listed below.
I recently purchase a 2003 BMW 330i with factory xenon lights that were manufactured by zkw. The light output of these headlamps is the worst by far I have ever seen from a modern vehicle. Xenon headlamps normally have superior brightness over halogen headlamps. My fog lights put off more light than the zkw headlamps. I know that this is not a bulb issue, because they bulbs have been replaced. The bowls that reflect the light turn brown because of the heat and light output goes way down over time, from what I have read on many forums. This is a major safety issue and BMW only sells the entire headlamp to fix the problem and not just the bowl that burns and discolors. The headlamps from BMW are over $1,000 each and I really can't justify spending that right now. Headlights are not a wearable item and I never expected to have to rep.
The zkw brand high intensity discharge (hid) / xenon headlights installed from the factory in to my 2003 BMW 330i degraded to a point where visibility at night was almost zero unless I drove with the high beams and/or fog lights on. Replacing the bulbs did not remedy the problem. The cause was burnt "reflector bowls" which are not replaceable. The whole headlight assembly must be replaced at $1000-1300 per side. I had the headlights repaired by a specialist (at a cost of nearly $700) as I was not ready to pay $2600 to replace the headlights with another set of zkw assemblies which would no doubt fail like every set of zkw headlamps installed in 2003-2004 330i sedans. I do not feel that headlights should be a 'wear and tear' item. They are obviously a critical safety component. The deterioration of light output is slow and takes time, so people may not realize anything is wrong with their headlights until they are driving with almost no output on the road.