Adding Cruise to my 2003 E350 SD. Boy was I confused when I first got started. But here's what I've learned so far and I believe it applies to most 150's, 250's and 350's and probably trucks as well.
First off there appears to be three generations of cruise controls systems 97 and earlier,(vacuum system) 98 -2004 (Servo Stepper motor) and 2005 up (fly by wire). Diesels are a different system all together.
2005 and up should be an easy add, just need wheel with buttons and the correct clock spring. Possibly would need programming of the vehicle computer. This system would use the same stepper motor that the throttle uses. Fully controlled by the computer. Fly by wire!
98-2003 not as easy. Based on my current knowledge while trying to keep all parts NOS.
I will need new wheel with buttons, I used a OEM 97-03 FORD F150 EXPEDITION GRAY VINYL STEERING WHEEL w / CRUISE CONTROL many truck and van steering wheels in these years should fit.
COVER AND CONTACT PLATE ASY F8UZ-14A664-DA w/ airbag w/ cruise this will plug into the existing factory harness and provide the wiring for horn, airbag and cruise.
A speed control servo actuator(YC2Z-9C735-AA) seems tough to find as well. Interestingly a guy on youtube used a Taurus actuator and it worked. The actuator is actually 3 parts, circuit board, motor gear assembly, bracket. The motor/gear assembly appears to be a interchangeable part. The circuit board may also be a interchangeable part, I'll check it closely to see if I can figure out if it has any chips that are programmable(there may be vehicle specific programming in the board).
The brackets are vehicle specific as well as the actuator cable depending on the throttle body connection. I think I found a new NOS cable XC2Z-9A825-BA this would be for a 5.4 gasser. It would appear that the servo end of the cable is identical on all the servo actuator cables. The engine end changes depending on the throttle body. If anyone knows which vehicles used the 5.4 that cable may work as well. There's always the possibility of fabbing a cable end to work possibly with aircraft hardware. The shop manual indicates the cable is pulled 10mm max in operation.
additionally there are two possible Speed control cutout switches these are easy to find 1 type plugs into the brake system master cylinder. I've found references to a brake pedal type. The switch is a NC circuit so its possible to just jump the connector for testing. If you have skills you could cut new threads in the MC casing (there's a undrilled spot for it) for the switch or add in a tee, (street Tee) in a brake line, I'm still not sure but the thread size looks 1/8 but no taper. The OEM way would be to just change the MC with a new one for a vehicle with cruise.
Finally there is a Ford service bulletin you can find by Googling TSB 06-8-5. This give good detail on the built in diagnostics. It uses the speed control indicator light to flash codes. Some say their cluster dont have it but more than likely it does. It wouldn't make sense to have different injection molds, the bulb may not be installed or even the correct wire for it but it would be possible, service data indicates its a GND signal from the servo. I found mine using a flashlight lower left in the instrument cluster. looks like a clock icon almost.
Most importantly is that the wiring harness for all this is in place look for a wide 10pin connector located under the coolant tank mounted on the fender, there will also be a 2pin connector for the MC speed control release switch next to it!
I'm still waiting on parts but with any luck I'll be able to cruise soon. Still not entirely sure what the main computer interface look's like. I think it operates as more of an interlock to allow cruise to activate, several other items must be correct for it to allow cruise ON, like brake light circuit, VSS signal, etc not entirely sure, programming may be needed, but likely it its already active.
If anyone has more to add please feel free, or to straighten me out on my mistakes.