Alternator???

I have a 99 windstar 3.0L. Lately I have a weird problem. Sometimes when I start the van (after a cold night, or after it sat for a couple of days) I notice that the dash lights are about 1/2 the brightness, the wippers move slowly and the heater fan is half strength. The engine is idling at about 1400 rpm (normally for cold start). Then anywhere from 15 seconds to a minute later suddenly the the dash lights brighten, the heater fan and wippers return to normal. I assume that the issue is that the alternator has not kicked in yet and that the whole system is running off of the battery until seconds later when everything appears to suddenly return to normal. Once, when this set of events occured I noticed that the battery light flashed at the moment that full power was restored. I haven't heard of this type of alternator failure before, I thought that either it worked, or it didn't, not this intermittent failure. My questions are these.
1) Is there a switch of some kind that turns the alternator on upon engine start? Is so could this be the issue?
2) Does this sound like an alternator failure issue, or the PCM?
This occures too fast to get out, pop the hood and put a meter on the battery to verify battery voltage. When operating normally the battery voltage is just under 12v with the engine off, and 14.7 volts when the engine is running.
I don't want to replace the alternator if indeed there is something else in the circuit which could be the issue.
I thank you for your assistance in this regard.
Randal

daveran2008,

I have a 3.8 1999 and experience the same issues. Interiot lights, dash lights, headlights, dim and go back to normal. I thought it was the alt, so I replaced and still have the same problem. It maybe the relays in the engine compartment fuse box. I was told to replace the PCM relay (302)first and go from there. I got one of each type of fuse and will replace each seperately to see if I can fix problrm. Won't do until Spring though. Too much snow around here. Was also told it could be the headlight switch which gets too hot ? Don't think its that however. If you find it before I do let me know ?

AvalonJohn

How old is the battery?
A weak battery could do that.......and if that is the case....it is likely placing a major load onto the alternator.......

The battery is 2 and a half years old and it appears to be working ok.

Thanks wiswind. I have been monitoring the battery since posting this. every morning before starting it was between 11.7 and 11.9. One morning my wife started the vehicle while I held the voltmeter on the battery and while starting the voltage droped to 9. I had the battery and system checked three times. They did a complete check of the charging system and battery and because the battery was continually low in the morning they replaced it. As the alternator and starter checked out as being OK I can only assume that the problem was with the battery. Although the battery continued to pass the tests, the machine continued to say that it needed a charge, so for some reason it was not holding a charge. Have you heard of this condition before?

Batteries fail in strange ways.
I figure that anything over 5 years on a battery is borrowed time.
I replace my batteries at 5 years.....to avoid problems....as the most likely time for a problem to show up is during cold weather.
Also, a battery that is always looking for a charge is placing a additional load onto the alternator.
Of course.....batteries can last MUCH longer than 5 years, but that is really their designed life.

The strange thing about the issue is that the battery is only 23 months old. It was a Walmart Energizer battery. They replaced it for free, and this one is noticabley better. It seems like a small battery for this type of vehicle 610 Cranking Amps. I'll be watching it in the future.