The Mercury Grand Marquis is a heavy, full-sized, V-8 sedan that seats six passengers. Though the Marquis lacks many of the features of modern luxury vehicles, such as a premium sound package and navigation tools, it does come standard with a leather interior, 17-inch alloy wheels and an automatic dimming rear view mirror. When the alternator in your Marquis begins to weaken or experience problems, you'll notice a lack of power and difficult cranking as it's the alternator's job to supply the battery with charging power.
Test the alternator with a voltmeter. Clamp the voltmeter's positive lead to the positive battery post and the voltmeter's negative lead to the negative battery post. The positive and negatives are color-coded for easy identification: the positives are red, and the negatives are black.2
Crank the engine and check the reading on the voltmeter. An alternator that's producing the right amount of energy will show a reading of between 13.6 and 14.3 volts. If the voltage is lower, it requires further testing at an auto parts store.3
Inspect the alternator for signs of aging and wear, such as corrosion or damage.4
Check the connections of the battery cables to the battery posts. Make sure the connections are secure and that there is no corrosive buildup. Even a healthy alternator will wear down quickly trying to deliver electricity through faulty connections.5
Listen to the alternator while the engine is running. A noisy alternator can indicate a loose or bent pulley, shorted diodes or bad shaft bearings.