The brief
The B200 had a headlamp bulb out and a brake light bulb gone, the kind of thing that's easy to miss until someone points it out or it fails a check. He brought it in to get them sorted, which is the right call, a dead headlamp and a missing brake light are both safety and legal issues, and a brake light especially is one the people behind you rely on. Bulbs are a wear item, they have a working life and they blow, and on a modern Mercedes it's worth fitting the correct spec so the lighting and the warnings behave as designed. The B200 just needed the blown bulbs swapped for the right ones and the circuits checked while they were at it.
The diagnosis
A check confirmed it, the headlamp bulb on one side had blown and a brake light bulb was dead, with the wiring, the holders and the fuses all fine, just the bulbs themselves at the end of their life. Nothing deeper, simple bulb failures. So it was a bulb replacement, the correct spec for each, fitted properly and the lighting checked all round.
The work
The blown headlamp bulb was replaced with the correct genuine spec, handled cleanly so no oil got on the glass, and the dead brake light bulb swapped for the right one. The holders and connections were checked, and the full lighting set, headlamps, brake lights, indicators, reversing lights, run through to confirm everything worked. A check confirmed both headlamps bright and aligned, all the brake lights lit, and no warnings on the dash.
The outcome
Both headlamps working and aligned, all the brake lights lit, the rest of the lighting checked and clear, and no warning on the dash. The B200 went home with the lights sorted. A blown headlamp and a missing brake light are small jobs but real safety ones, so swapping the bulbs for the correct spec and checking the lot put it right.