Toyota Repair: Locking Differentials not engaging, motor actuator, locking differentials

Question
I just bought a 1996 Land Cruiser with 99000 miles and the locking differential lights keep blinking without ever locking.  High and low-range both engage and the center-lock light light comes on when the transfer case is put into low. I've run the transmission through the range of gears without them locking.  Will this be something akin to a vacuum pump going out?
Any rough estimate on how much to fix?  

Answer
There may be a problem with the center differential lock control relay or the motor actuator on the transmission, in any case I have not experienced this condition so I don't have an easy solution for you, I would recommend having the toyota dealer diagnose it.