The alternator keeps the car battery charged and is powered by the engine drive belt. The Ford Focus is a compact model, so removing the alternator from the engine can be tricky due to the smaller space in the engine compartment. The removal process will vary depending on the year and engine type, so consulting your mechanic is highly recommended.
Disconnect the car's negative battery cable.
Detach any shields blocking access to the vehicle; remove their bolts with a wrench. This may include the heat shield for the alternator or exhaust manifold and the splash shield underneath the engine.
Remove the engine drive belt--turn the bolt on the drive belt tensioner to relieve the tension and slip the belt off the pulleys. Verify that you know the path the belt must follow along the pulleys before you do this.
Disconnect all other parts from the engine that obstruct access to the alternator. This varies greatly depending on the year and can include the expansion tanks for the coolant or power steering fluid and the air cleaner's intake tube. Most of these parts have bolts that require a wrench.
Remove the bolts for the alternator with the wrench and remove it from its engine mount or bracket. Take note of where each bolt was installed as you must put them in the same place as before.
If you are replacing the alternator, remove the old one before you purchase the new one. The replacement must be the same as the old one, with the same identification markings and the terminals having the same size and location. Also, the shop may need to transfer the old alternator's pulley to the new one.