'95 4WD issues 4X4 light flashes 6 times

[gts]

My parent's have a '95 explorer 4.0L. When you put it in AWD it won't go in until you come to a complete stop. It also won't come out until you come to a complete stop. The 4WD light also starts flashing 6 times then a long pause then 6 more times. Dad's taken it to the Ford garage and they say there is no codes with 6 flashes for this year. I don't know if there is a cut off mid year but it's an early '95 if there is such a thing. Any help would be great as I'm driving it right now being the tranny in my '97 Explorer is acting up. I'd love to be able to fix this for them while I have it.

 

[gts]

OK so after doing a bit of reading on this site I'm coming to the idea that maybe the speed sensor for the front output shaft is not getting a signal and therefore not allowing the transfercase to lock on the fly but only when you come to a stop. Also what makes me wonder this is because I had it out on the beach over New Year's Eve and it seemed to go into 4X4 but the traction control didn't seem to work where before in the snow I could feel it transfering power back and forth to the wheels that were slipping or spinning. So my guess is because it's not getting one of the speed inputs it's just locking into 4X4 and not functioning like normal.

Now my qestion is where is the sensor for the front output shaft? Is it a sensor inside the transmission or does it use the front wheel speed sensor from the ABS system? I assume it uses the VSS for the rear output shaft speed and it must be working as the speedo works.