So a friend of mine has a 2005 Taurus that would not start, changed the battery. After changing the battery the battery light was on and the display indicated check charging system. Both would go off if the engine was reved up. This is when the car was brought over to my house.... I checked the battery voltage with the vehicle off and again when it is started and it was 11.9 each time. Nothing changed even when the motor was revved up. Ok, sure seems to be a bad alternator. I had a new alternator off of a 2001 Taurus that I threw on. I do know that the part numbers are NOT identical between these vehicles but they look and hook up exactly the same. I assumed that there was a minor and hopefully irrelevant variance in maximum output. So now I start the car and the display indicates a charging system problem and the battery light is on all the time regardless of engine RPM. But what is really odd is the new alternator is charging with battery voltage @ 13.6 when running. Now I do know that most modern cars usually have a running voltage of about 14-14.2. Is this enough to make these warnings appear? I am guessing that it should be adequate to keep the starter working and the car running but will harm come to the car? Does anyone know what the 3 wires on top of the alt do? Is it possible that the three wires are in a different position between years and is causing the warning light problem? I hate tell her to spend the $200.00 for the proper alternator without knowing if it will even cure the problem.