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There are a couple wires that plug together near where the hood meets the front fascia. Mine has come unplugged before you might want to check this. If it isn't that the bulb probably needs replaced.
If you bought from a dealer and it was in the showroom, many unplug the light under the hood. I never plugged mine in on the C4, and my C5 is currently unplugged. The plug, as stated previously, is on the passenger side. Just trace the wires down from the light and you will find it.