Converting a W203 to Bi-Xenon is a plug-and-play direct interchange after you remove the bumper cover. There are no external parts. If the car had the earlier single xenons then you are done. If it didn't, the bi-xenon feature must be enabled at the dealer. Keep in mind that if the car did not have xenons before, the headlight self levelling won't exist because the front and rear level sensors will not be present. Whether the connecting wiring will be in the harness is unknown to me.

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Roger E.