2004 Ford F350 4 wheel drive

you need to find out if the drive shaft is turning when you engage 4 wheel. it could be the vacum pump under the hood or the vacum lines to the front hubs. 'the rubber lines that are next to the brake lines'' or it could be the shift motor on the transfer. if you put it in low range you shoud hear the gears in the transfer move. if not the motor is probibly not working if you hear it move try turning the lockout on the front axles'' by the tires on both sides'' see if that works. if the lockouts work it is a vacum leak. if none of this works by a dodge