The Mercury alternator is an essential part of your vehicle. You literally, can't do anything without it. Your moon roof, air conditioner, high-amp stereo, and heated seats all feed off of the alternators power. The battery cannot be recharged if the alternator isn't working. Old alternators only needed to send out about 60 amps of power. The modern alternator uses at least 100 amps to power all the amenities in your vehicle. Now that you know how hard your alternator works, you can understand why it can stop working. If any major part of your alternator (the rotor, stator, ignition coils, or diode packs), goes bad for some reason then you can count on having to replace the whole thing. Other minor parts of your alternator, such as the alternator belt, can break and be replaced without forcing you to buy an entire alternator. Make sure to rule out your battery as the source of the problem before going out and getting yourself a new alternator.