The alternator inside the engine bay of any Ford or Mercury vehicle serves essentially the same purpose as the generator did in older cars; it is the electrical power plant for your automobile, turning the mechanical energy of your engine into electrical energy you can use to run your headlights, taillights, radio, etc. When the alternator no longer works properly you will begin to lose the ability to use these electrical systems and the battery will no longer be recharged. Soon, you will not be able to start your car.
Open the hood and disconnect the negative (black) battery cable from the negative terminal on the car's battery.
Pull the belt off of the alternator pulley by first turning the tensioner pulley (just under the alternator) clockwise, using a socket wrench, then using your hand to pull the belt off of the alternator pulley.
Disconnect the two wiring harnesses from the alternator. Both of them simply snap in, so just depress the tabs and pull out the harnesses.
Unbolt the three bolts holding the alternator in place, using your socket wrench.
Remove the old alternator and replace it with the new alternator. Bolt it into place with the three bolts you removed in the previous step.
Push the two wiring harnesses into the new alternator.
Turn the tensioner pulley clockwise again, using the socket wrench, then place the belt back over the alternator pulley.
Reconnect the negative battery cable to the negative battery cable.
