2003 Ford F-150 will not engage in 4 wheel drive

Hello,

Check the Motor on the transfer case it looks like this...

Ok,

On the front axle there's an Actuator Motor it is Vacuum Operated. Check the vacuum lines

Ok, are you able to raise the vehicle off the ground, all 4 wheels, safely? If so once you have it off the ground have someone inside start it hold the brake then put it in 4 wheel drive and slowly release the brake. Look under the vehicle is the front drive shaft turning? If not have person in vehicle hit the brakes put in park and turn vehicle off, Then with a vacuum gauge attach it to the actuator and apply 10 - 12 psi of vacuum. Start vehicle and put in 4 wheel drive if wheel turn then you have a vacuum leak. It is most likely a small leak just enough that the 4 wheel drive won't engage.

If the front drive shaft does not turn then the problem lies either in the transfer case motor or the transfer case itself.