The Ford Focus uses an alternator to run electrical devices in your vehicle while the engine is running. A voltage regulator maintains a constant voltage level and is frequently integrated into the alternator assembly. If your battery continually runs down or your headlights become dimmer while the engine is running, you may need to replace the alternator.
Determine which alternator your Ford Focus will need. You'll want to be sure the new alternator is compatible with your Focus's engine. Models made from 2000 to 2007 can be equipped with a 2.0 L or 2.3 L engine. Models made after 2007 will have a 2.0 L engine.
Disconnect the negative battery cable with a socket wrench. Remove the accessory drive belt and the electrical harness for the alternator.
Remove the coolant expansion tank and power steering reservoir. Use a socket wrench to disconnect the bracket for the engine wiring harness and the ground cable. Take off the purge valve for the evaporative emissions canister if your VIN begins with 3 or 5. If the VIN starts with P, you will need to remove the power steering pipe brackets and heat shield for the exhaust manifold.
Take off the mounting bolts on the alternator with a socket wrench and detach the alternator from the vehicle.
Install the new alternator assembly and tighten the mounting bolts with a torque wrench to 18 foot pounds for a 2.0 L engine with a VIN that begins with 3 or 5. Torque the mounting bolts for a 2.0 L engine with a VIN that begins with P to 35 foot pounds. Torque the mounting bolts for the 2.3 L engine to 35 foot pounds.