1. Unfasten the negative battery cable of the Mercedes 300SD from the battery post with an open-end wrench. Locate the alternator directly behind the radiator on the passenger side of the engine compartment.
2. Loosen the bolts that secure the alternator to the engine and bracket with a socket wrench -- just far enough that you can move the alternator on the bracket. Move the alternator forward and remove the alternator belt.
3. Remove the electrical wiring plug from the side of the alternator by hand. Unfasten the bolts that attach the ground wire and the electrical wiring harness to the alternator with a socket wrench.
4. Detach the bolts that secure the alternator to the motor and bracket with a socket wrench until you can slide out the bolts by hand. Lift the alternator off the bracket and remove it from the engine compartment.