Hello from a first timer.
My 2001 Ford Windstar has 208,800 plus miles. Last June of 2009 while in Florida the battery and original alternator were replaced due to age and lots of use. Things were okay here in Cleveland, Ohio till December of 2009 when the battery light began it’s erratic appearance and would not turn off unless I restarted the engine. The NTB store is national and they replaced the alternator saying that some relay in the unit was defective. Thank goodness for warranties. Just this month the battery light problem reappeared and any use of ammenitiies dimmed as if there were fewer volts available. Yesterday I took the Windstar back to NTB and they could not find any obvious problem. All electrical checked okay, no loose or corroded wires stood out. The computer check showed four pending codes of B1676, B1470, B1260, and B1246. One was for the headlamp I replaced the day before. A second was for the ignition key being out of range (he said there’s a battery in it?). A third was for corroded wires going to the dash. And the fourth was never discussed. The mechanic sent me home with instructions to take two aspirin and go to bed till the light returns and then to drive directly to NTB leaving the engine running so they can deal with it from there. My wife is scared because we do alot of long distance driving. You expert mechanics out there, what’s the scoop?
Thanks 
walking joe
You need to see a mechanic. Something in the electrical system is causing a deep battery drain. It’s been my experience that the electrical system will usually fail at the longest distance from help.
Have the alternator checked for a weak or failed diode, common with “rebuilt” alternators as they seldom replace the diode trio unless they have to…