Hello from a private lake in NW WI.
Friend had a Ford that was nickel n diming him so he put out to pasture in his swamp.
Was a 99 F150 XLT with only 80k on it that I picked up for my cousin who had a Ford crate motor let go on him while travelling cross country and was in a hurry to get his truck on the road.
So picked it up for him thinking we would do a quick motor swap then he sells his completely rust free Lariat from Montana for $3500 and passed on motor swap idea, if I had know would have bought his truck off him, paint was everywhere underneath, new rear axles, transfer case, tires, etc.. He was heading to new job and employer said just rent a vehicle and they will pay for everything...
This left me with a rusty Ford to add to my collection of rusty cars and trucks already in my collection.
My cousin test drove and ran scan tool and told me GEM was bad, so without ever driving it myself was first project, now dealing with 4x4 not working correctly and deciding if should swap back, think will troubleshoot it first as that GEM was not fun to install with bad back..
Rear brake had locked up when he test drove it to see if motor was worthy so I never got to drive it just toss money at it.
Rear axle seal leaking on ceramic brakes caused the locking up, ended up with new Timken bearings n seals, then spiders were noisy so swapped them to discover cover rusted through, so ended up all new brakes, parking brake cables, bearing seals n spiders...
I can see why my friend gave up on the old gal, but she is up and running and will use forum to help with the 4x4 issue and whatever else I run into.
I mainly had older Fords, since we had dealership in town here, Mustangs, 3-4, 1 wish never sold, 428 SCJ 428 with 4 speed and fastback, then a 68 Torino with the 390 with some cobra jet package, and a 68 F100 custom I put a built up 352 into, so that was my early years.
Moved onto Pontiacs for decades, Chevy Trucks n Vans for scrapping n rummage sailing, had an 89 F150 for a few years that never let me down, always enjoyed the ride of the Fords over all the rest in trucks, always smoother experience. My 77 K20 plow truck is like a chiropractor experience without the plow, so this 99 F150 will be easier on the old bones once fixed up...
So there you have it, a quick story about me, hope to give help as much as I get some help here, was mechanic at Ford dealership for few years then out on my own for 15, and a wrench in my hands since I was in kindergarten, so lot of experience...

 

Welcome!

 

I think the 4x4 diag starts in part 2.

 

Watched the vids , prob should continue this in some specific forum page, but code P1876, both solenoids getting ground signal regardless of what position switch is in, live data shows switch working.
Had another issue when got truck , if left timer delay relay for lights in fuse 14 would pop and no power windows so just pulled that relay so had windows. So there is some short somewhere, rockers wasted, harness that runs alongside or under parking brake all 'looked' good.
Will search forum for that code, also noticed even with charge of freon AC does not kick in, just got it mechanically worthy, now to get into electronics...

 

Check the clutch gap on the AC compressor. If it's too wide, the clutch magnet can't pull it in.

 

The clutch gap should be around a business card in thickness.