Ford Repair: 04 Mercury Sable charging system light coming on, remanufactured alternator, mercury sable

Question
My mother is having a problem with the charging system light coming on occasionally while the engine is at idle and sometimes while driving at highway speeds.We recently put on a remanufactured alternator and replaced the battery, before the light started coming on. she has taken it to the local parts store for a diagnosis and it shows that everything is working correctly. We cannot figure out why the light is coming on. It always starts fine and runs fine while the light is on with no obvious problems. Any ideas?

Answer
probably the alternater but without checking i can't say but there is a lot of junky rebuilt parts out there. be sure and check the connector on the back of alternator and make sure they are tight-look at the pins in the connector make sure they aren't spread apart causing loose connection-then take it to a repair facility you trust and have it checked. putting a voltmeter or tester on it for 3-5 minutes isn't a good test.