first of all let me say this seems like a great site so far!! I have a 2006 F150 and when I turn the 4wd shifter to four high the light flashes on for an instant and then it seems like 4 high isnt engaged all the way judging by the clunking noise but it goes in and out of 4 low perfect Any Ideas? oh yea it did work fine a time or two yesterday but now it is back to doing the same thing

 

now the lights are coming on like they are supposed to the majority of the time but its still not kicking in I cant figure it out and hate to take it somewhere that wont do anything but just start replacing parts

 

your system uses engine vacuum to engage and disengage the hubs at the wheel ends. there are solenoids the open and close to cut off the vacuum.. read this.


https://www.ford-trucks.com/forums/8...then-some.html