I have a 2004 F-150 Non Heritage. The 4WD was working fine last year and is not working now. The light on the dash comes on and I do seen to be getting vacuum at the hub but it is not engaging. Several months prior to using the 4WD I did do some front end work and must have knocked the vac line off. It was off for several months, I reinstalled it and it is still not working. I could use a little help/guidance on where to go from here?