Why does the four wheel drive light sometimes flash on and off while driving in a 1996 Ford Aerostar?

Mine does it, too. The flashes are a series, decodable just like the self-diagnostic codes from the Check Engine light: a series of flashes, a pause, and then a second series of flashes, a longer pause, repeat. I have been unable to findany information as to what the codes are or mean. However, usually it means that the AWD computer is not receiving a signal from one or more of the wheel sensors. Check the wiring to ensure that there are no breaks.