There are a number of different ignition components present in vehicles that are necessary to allow the engine to start. All of the parts in your Mercedes' ignition are working together to help your engine run efficiently. These include things like your battery to the starter motor and spark plugs. Spark plugs are parts responsible for generating a bolt of electricity at a certain time so that the combustion process can take place. In some vehicles, depending on what kind of engine you have, you might have glow plugs instead. Glow plugs work the same way but are built for diesel engines. They work to help preheat your engine's cylinders so the combustion can occur easier. There can be problems with both spark plugs and glow plugs over time, and regardless of what your car has, the symptoms are the same. Misfiring of the engine can occur and reduced performance. You also might experience hard starting. We sell OEM Mercedes glow plugs and spark plugs here on our site.