There should be a gray plastic "door" on the backside with a metal wire running up/down on the inboard side of the headlight housing. This metal wire will unclip and the door will hinge off from the outboard side (you might have to remove your washer reservoir to access the driver's side). The H4 bulb will be held in by a retaining (can't remember if its a wire clip or plastic ring, forgive me). Remove and replace. Don't touch the glass part of the new bulb.

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too many w123's
84 280 SL 5 speed