The solenoids appear to be working as they should.What us the double click that you hear in the dash after you put the truck into 4x4. I am hearing this clicking and seeing the 4x4 light on the dash just before i start to hear the front diff try to lock up.Is there some kind of solenoid or switch inside the dash that may be malfunctioning?

 

Only things in the dash related to 4x4 is the rotary switch if ESOF, and the GEM module. There will be fuses/relays in the fuse box.

 

the solenoids seem to be working hard to tell you shift to 4 wheel it goes to 4 wheel you shift to 2 wheel it goes to 2 wheel. the problem is that as you drive in 2 wheel drive you hear the double click in the dash of the truck as the 4x4 light comes on and trys to engage the front diff i assume.if you shift the truck into 4 wheel drive the dif engages and the noise stops and the truck goes into 4 wheel drive as needed,the problem being i didn't want to put it into 4 wheel in the first place.What is the clicking noise that you hear in the dash as you wait that few moments from when you pull the shifter into 4 wheel and it actually goes into 4 wheel drive. Is this some switch up in the dash that could cause a problem.Remember the truck goes into 4 wheel and out of 4 wheel fine the problem is the truck seems to want to go into 4 wheel drive all on its own.Your answers are great but not addressing what is really happening in my case.Maybe this is something nobody has had happen to before.Sorry for being a pest.

 

I may have figured this problem out....the 4 wheel drive indicator switch on th e transfer case may be sending a bad signal to the 4 wheel drive vacuum solenoids that activates the front diff fork that puts the truck into 4x4.I put the truck in 2 wheel drive and unplugged the electical connections on the solenoids and the vaccum held no 4x4 engaging problem.Am going to change the switch($50+canadian)and see if this fixes the problem if not solenoids next ($150+).Let you know if this works,getting this problem narrowed down.Later.

 

kingfish51....question....99 f150 xlt 4wd 4.6 maunal trans and manual 4wd shift. Ive switched the vaccume hose down on the vaccume motor and I can get the thing to engage.....I cant understand if when u switch from 4wd out to 4wd in... is the vaccume suppose to switch or what.? Do those solenoids on the firewall by the battery go bad..? I get voltage there but it doent change when I do the in/out switching of 4wd. I did blow out the vac. lines...there not plugged. Is there any relays to check or fuses....Thanks for the help....If u can.