I have 1999, F150 5.4L with electric 4wd shift ****. I put it in 4high just fine and smooth. Now 4lo on other hand rough shift if it goes in 4lo, sometimes won't engage but 4 high works fine. What's the cause

 

Is the transmission in neutral with your foot on the brake?

 

you should be stopped, in neutral, or might need to roll the truck a foot to get it to engage........ If it JUST DONT WORK... then you have an electric motor on the transfer case that shifts from LO to HI and that is not happening.. Either stuck / bent/ motor problem/ wire problems.