After you have determined your vehicle is equipped with a 3g Ford alternator from the 3g application list, it’s time to diagnose the charging system. The most common symptom of a 3g alternator failing occurs normally between 90,000 to 130,000 vehicle miles. Alternators occasionally fail before this time, and some alternators last past this time, but the largest percentage will fail between these two numbers. You’ll notice the idiot light came on, then went back off again. This may occur simultaneously with the turning on of an accessory, or seem to happen inadvertently. This scenario may occur again soon, or may reoccur sometime later. If the vehicle is equipped with a voltmeter, you should notice it dropped lower than usual or seemed to fluctuate. Having the alternator tested when the idiot light is not on, seldom reveals any valuable information. Alternator problems occur 99% of the time while driving the car. If your battery is dead after the car has sat for several hours, but starts back up after the car sits for only a couple of minutes, it is only a 1% chance that the alternator would be causing this.
Now is the time to do a few basic visual checks on your vehicle.
1. Look closely at the alternator itself. Is it the original alternator that was on the vehicle from the factory? Does it have the same age appearance as the other engine parts near it? (Notice the dirt or corrosion). The original equipment (OEM) will not have any stickers or writing on it whatsoever. If we can determine the alternator is OEM, we can make a decision on whether to rebuild the alternator based on logic, and by observing the odometer (most 3g alternators fail between 90k-130k) and guessing that the alternator may fail soon anyway.
2. Remove the battery (negative terminal first) from the vehicle. Clean all the connections and clean the exterior of the battery. Take it to a battery vender for charging and assessment no matter what condition it seems to be in.
3. Visually inspect the general condition of the wires surrounding the alternator and the serpentine belt. The belt’s condition (other than being cracked or oil soaked) can be most accurately assessed by observing the alternator pulley. Is the pulley rusty? Is there belt dust or debris on the pulley, or the front of the alternator? This is a sign of a failing self tensioner device, or just a worn belt. This is NOT a sign of alternator bearings failing.
4. Assure that no pollutant material such as oil or antifreeze is near the alternator. An alternator is designed to pull air as a coolant through it, so anything within 12 inches of the alternator will eventually atomize and end up on the inside of an alternator. Oil quickly breaks down the carbon/copper content of the brushes and causes failure. The only thing worse than oil is antifreeze. Antifreeze literally destroys everything in an alternator.
5. Dash lights and headlights dimming and brightening with RPM could be alternator or most frequently a combination alternator/belt/battery.