Glow plugs in a Mercedes are used in place of spark plugs. This is because Mercedes uses a diesel engine instead of a regular gasoline engine. Glow plugs heat the fuel inside the combustion chambers while the compression of the engine ignites the air and fuel. Over time, the glow plugs wear out and need to be replaced. The first step, however, is removing the plugs.
Open the bonnet and remove the glow plug wires from the top of the engine. While you will be replacing all of the glow plugs, only work on one glow plug at a time. Consequently, this means you should only remove one glow plug wire at a time.
Span the glow plug socket onto the square end of the socket extension and lower the socket into the glow plug well.
Orient the socket so that it grabs onto the top of the glow plug. The socket has a rubber interior that will grip the glow plug and hold it in the socket.
Turn the socket extension, socket and glow plug counterclockwise with a socket wrench to loosen the glow plug.
Pull the glow plug out of the engine with the socket and extension.
For specific information about removing your Mercedes glow plugs, consult the particular vehicle's manual.