New information in Post #8. (posted March 19 2020) see below. Cruise is sort of fixed. Everything I did before post #8 was not the solution. There is some kind of switch or resistance issue with the buttons I don't quite understand how to solve.

Below is the older information that I now don't think is the problem although could still be helpful to others. If your cruise control wont engage but everything looks ok, maybe check post #8 before you tear your truck up like I did searching for ghosts.
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I have a 1999 XLT with the 5.4L V8 and about 3 years ago I had a re-manufactured engine dropped in to replace the old one that had about 160k miles. I had a rod fail and the bolts that hold it on the drive shaft came off or broke.

When I got the truck + new engine back, the cruise was working. It has only started acting up in the last 6 months. The only work I have had done on it that may coincide with the cruise failing is the AC. I had a new compressor and condenser put in last year. The cruise cable looks fine and I can pull on the cable at the servo motor and it pulls the throttle as it should. As for the cruise itself there are no lights on my dash that indicate if it is on or off so feedback is minimal other than the truck holding speed after i take my foot off the pedal. I have heard about holding the "Cancel" button on the steering wheel when turning the key to run to get into a cruise diagnostic mode but my model either doesn't support this or something is wrong. The cruise is totally inoperative now and here is what I have tried.

Fuse F7 under hood is good
Fuse 5, 13, and 15 in the cab are good
Horn honks and the airbag is still original and has never been activated. Clock spring seems good (side note: why dont they call that a slip ring? clock spring sounds odd on a car)
All the cruise buttons light up when the headlights are on

For reference, here is the pin-out I am using when probing the servo motor module:

Pin 1 - Speed control indicator lamp Output
Pin 2 - not used
Pin 3 - Vehicle speed sensor input
Pin 4 - Brake pedal position switch input
Pin 5 - Speed control switch input
Pin 6 - Speed control switch ground
Pin 7 - Power in
Pin 8 - not used
Pin 9 - Speed control deactivation switch input
Pin 10 - Ground

I have unplugged the harness from the servo module under the hood and measured the resistance across pin 5 and 6 (2 most middle pins) of the harness and get all the correct resistances for each button press.

Coast = 128 ohm when pressed
Resume 2230 ohm when pressed
Set = 678 ohm when pressed
Off = near 0 ohm when pressed

With the harness still unplugged and the key out of the ignition switch i read the following:

Pin 10 to ground shows near zero ohms
Pin 4 to ground also shows near zero ohms. If press the break pedal I see 12v
Pin 9 shows 12v

With the ignition switch set to run but engine off i read the following:

Pin 7 shows 12v
Pin 5 shows 12v when I press the "ON" button on the steering wheel

As for the master cylinder cut off switch, I see 12v through it when the breaks are off and read nothing when the breaks are pressed. (I have the recall upgrade cable installed)

The last thing I have poked around on is the servo itself. I've seen in some online forums and YouTube videos that the servo stepper motor locks up but in my case the motor spins just fine and the insides are very clean and no burn marks or distortions due to heat on the circuit board. I've even applied 12v to the solenoid that locks the gears to the speed cable and it clamps just fine. I'm not sure how to test the stepper motor though. Since its clean, dry, and no burn marks, my guess is its probably good. I tested the resistance between all the stepper motor wires and get this...

pin 1-2 = 4.9 ohm
pin 1-3 = 4.9 ohm
pin 1-4 = 2.7 ohm
pin 2-3 = 4.9 ohm
pin 2-4 = 2.7 ohm
pin 3-4 = 2.7 ohm

Since there are no open readings my guess is the motor is ok.

my best guess on the different resistances is that pin 4 is some kind of center tap line and the 2 extra wires to make it a 6 wire stepper motor are internal and cant be accessed.

Can anyone offer information on how to test to see if the VSS signal is good? My guess would be to hook up pin 3 (VSS) and pin 10 (ground) of the servo harness to a DMM and take the truck for a drive and look for a voltage change relative to speed? If that turns out to be a problem what would fix that?

Any idea if someone (dealer or otherwise) would be able to test the servo to see if its functional?

I cant think of anything else to try. Hopefully the steps I've listed can help someone though.

 

Has the recall been done? If so, there's an inline fuse in the harness attached to the disconnect switch on the master cylinder. If the switch is wet with brake fluid, it's shorted out and has blown the inline fuse. If the recall has NOT been done, take it in, it's a fire hazard.

Replace the switch and harness with this:

 

Like glc said, make sure the fuse is there, if not, I would disconnect the battery, especially if you park it inside your house.

 

I took the truck in years ago to get the inline fix cable added. that part is good and the fuse is intact. the pressure switch it attaches to is also good. i can see it connect and disconnect 12v at the servo harness when i apply the breaks.

 

The speed control self test was added around the 2000 or 2001 model year, it wasn't present on the 1999 and older F150s. Therefore, no light in the cluster.

You've checked all of the servo inputs (except one) and they appear to be normal. The only one you haven't checked is the VSS signal. Verify circuit #679 from its PCM output to the servo, repair if necessary. If that circuit is good and if you have properly working 4x4 (if equipped) I'd conclude the servo has failed internally.

 

Thanks for the info about the circuit to look for. I broke down and ordered the OEM repair manual and the wiring diagram manual to help. It wont be here for a week so ill try and report back what i find.

 

Final update:
I was in a junk yard looking for interior parts unrelated to the cruise and saw two trucks with their cruise servos waiving in the breeze so I pulled them. The first servo I installed fixed the problem. It would appear that the electronics on the original servo went bad somehow. When I opened the servo up, the original motor and solenoid were pristine and not seized. I could even actuate the solenoid manually but the system would just not wake up or respond to the button presses. It somehow feels like I cheated to get the solution rather than fix the circuit board. but with a 1/4 inch layer of conformal coating over every part of that board, I don't think it would have been very fun to probe around on that PCB. Well, at least i can cruise again!

 

After all this time has passed I've learned something new about my cruise control problem.

One day I was driving to work and had a thought to pull out the buttons in the steering wheel and disassemble them to see if maybe the buttons were failing somehow. nothing looked wrong and all the resistors and shorting paths were still good. I hit the contacts with contact cleaner and put everything back together disappointed yet again. There was no change after it went back together. On the remainder of my drive home I was rocking the switches back and forth repeatedly. I did that just to make sure the contacts were still making contact in the vain hope it might come back to life. To my surprise after about 2 or 3 minutes of doing that the cruise started working again. It worked flawlessly for that 30 minute drive. the next day however the system went dark again. I tried the rocking switch thing again and on a side note discovered that if i hit "On" at the same time as "Coast" the horn will honk. this only seems to work if i haven't brought the cruise back to life yet. but the rocking does bring it back to life.

What i don't understand is why. Those contacts look pristine and an ohm meter says they are giving the correct resistances or shorts. I'd hate to spend over $140 for new switches only to not solve the issue. I even pulled out the clock spring to test its resistance through itself and did not see much change in resistance (maybe 0.5 to 1.5 ohms).

there is something really fishy going on with my electrical at the steering wheel. To get at the clock spring I had to remove the key switch. once it all went back together I now have a one in four chance of the key not cranking the motor. Starting solenoid is good. I replaced it thinking that was the problem but the same mystery cranking problem persists. somewhere between the key switch and the solenoid I am loosing connection. I'm half tempted to just wire up a permanent starter button and just not deal with this new thing.

long story short, I don't know what to make of this latest discovery. I don't know what to replace now if I should go with new buttons or the clock spring or something else. The inside of my truck is very clean and as dust free as an F150 can be from that year. I don't think dust or grime is a problem. My best guess is that since the signalling for the cruise brain is resistance based, the switches are subtly adding some resistance after a night of rest. Maybe its just enough of a change to cause the cruise control to misread the resistance it sees from the buttons. The reason I think that might be the case is because the horn honks when i press "on" and "Coast" at the same time. However, that only happens if the cruise is not responding to the buttons. After I rock the switches for a few minutes, the horn won't honk anymore via the cruise buttons once the cruise starts working.

I've had those switches out and cleaned meticulously. in my line of work I work with surface mount electronics under a microscope. i can see a flaw on a fleas knee if i zoom in enough. with an engineering background, the near perfect resistance of the switch contacts, slip ring (clock spring), and resistors does not make sense to me.

Should I just bite the bullet and get new switches and or clock spring?