The Mercedes S430 (named for its 4.3L V-8 engine) is part of the Mercedes S-Class W220 body style, produced between 1998 and 2005. Replacing the headlamp bulbs is the same on all S-Class models made during this period. Despite its reputation as a high-tech--and sometimes difficult to work on--vehicle, the procedure for replacing the headlamp bulbs is quite simple, even when compared to some other vehicles. A few higher-end S430 models are equipped with bi-xenon headlamps; these do not use standard bulbs. Dealer replacement is required for bi-xenon headlamps.
Turn the headlight switch to the top-centre position to turn the headlights off, and then turn the engine off and open the bonnet. Determine which headlight bulb you want to replace. Each side has a low-beam and high-beam bulb. The low-beam bulb is used for normal driving (the most likely to fail--it's used more often); the high-beam is used for your "bright lights."
Search for the bulb cover on the rear of the headlight assembly. The low-beam bulb is the outward facing bulb on the assembly; the high-beam bulb is the centre bulb.
Push down the upper tab on the appropriate bulb cover. This will release the cover from the assembly. Set it aside. Behind the cover you'll find the bulb socket. On the rear of the bulb socket is an electrical connection. Unplug this connection.
Pull down the retaining spring; this wire holds the headlight bulb in place. Grasp the headlight bulb and pull it straight out of the assembly.
Insert the new headlight bulb straight into the mount (hold it by its base--not by the glass). Line up the notch on the bulb socket with the recession on the bottom part of the mount (low-beam bulb). For the high-beam bulb, line up the notch with the recession on top. Flip up the retaining sprint to secure the new bulb.
Plug the electrical connection back into the headlight bulb. Push the bulb cover firmly back in place to snap it back on.
Touching the bulb's glass can cause the new bulbs to fail. Take extra care not to touch the glass.