I have a 99 f150 and my 4x4 is not working. I have a new vaccume acuator on the front differential and a new differential installed up front but when i turn on the 4x4 switch nothing engages. The acuator is moving so i dont think its a vaccume problem. Any ideas?

 

I have the same problem and Im curious what other have to say so I can try on my 1999 F150. If your supper lucky it could just be the fuse in 104 spot under the hood. Dont use the plastic cover to see which one is 104 as the picture is inverted on the plastic, it can be a little confusing. Here is the owner manual on our 1999's look on page 154, it shows a diagram of the fuse box and list which fuse does what.

http://www.motorcraftservice.com/pub.../99f12og1e.pdf

My 4x4 light was staying on all the time even though it wasnt in 4x4. When I pulled that fuse (104) which was not blown and started up the truck the 4x4 light went off. When I put the fuse back in and started the truck my 4x4 light stayed off. I took it for a test spin and turned the **** to 4H and I heard a loud clunk. I tried to put it back in 2H and didnt hear anything and the 4x4 light stayed on. I think I may have a bad motor at the transfer case. Not sure. Any help would be appreciated.