This is from the poster 6SPD_soul-give him some rep points-not me
This should be a sticky someplace
I just had some issues with my CC and have sorted that out, but I found there is a really slick self diagnostic procedure for the cruise control. You don't need a diagnostic scanner to do this either, just the car. From what you describe I think the cruise control servo (motor with a spool of cable that controls the throttle body for CC) is bad, but this test will tell you for sure where the problem lies. This self diagnostic test will work on all Foci from 00-05, in addition to many other Ford models in those years.
The test is basically this: you're going to be turning the ignition key on and off repeatedly and then hitting the cruise control buttons quickly in a specific sequence, and then the cruise control light will blink repeatedly, and the number of blinks tells you where the fault is. It's easy to do once you get it sorted in your head and you won't mess anything up if you don't get it right the first time.
If it's a manual, don't depress the clutch. If it's an automatic leave it in park. First, turn the ignition to the accessory/run position but don't start it. Press and hold the CC off switch and then repeatedly turn the ignition from run to off and back to run again, you should do this 3 or 4 times. End this sequence with the ignition in the run position and then let go of the off switch, and you should see your CC light blink once, which means it's ready to run the self diagnostic. If it flashes 5 times at this point then it's a faulty speed control module, which is that servo I mentioned above. Quickly after the light blinks (like a second after), you then need to hit the other cruise control buttons in this order, and you will need to hit them fairly quickly for the test to proceed:
The CC light should blink once after each button you hit. Kind of take your time hitting the buttons and it's easier to keep track of the flashes, which is important at the end because you need to count the number of flashes that come after you hit "set". There won't be an immediate flash after you hit "set", there will be a slight delay, and then will come another short series of flashes. This next part is all verbatim (except for the parenthesis) from the Ford guide I'm translating here.
0 Flashes (no flash after last button is pushed): suspect circuitry or speed control steering wheel switches.
1 Flash: Static test passed (cruise control should work)
2 Flashes: BPP (brake pedal position) switch is damaged, circuit is damaged, or the brake or clutch pedal was applied during test.
3 Flashes: Brake deactivation switch is open or circuit is damaged.
4 Flashes: Indicates the speed signal circuit is open or damaged (wheel speed sensors, ETC)
5 Flashes: Suspect circuitry or module.
So I guess try to run the test. It's pretty quick and easy once your thumbs get the button sequence down. Then you should at least have a better idea where the problem is coming from. Post back here with results, I'm curious where the problem is for you. Mine was the brake deactivation switch which I'm putting in soon.
Yeah, the above was my post and you should run the test, but there is a vehicle speed sensor that reads off of the transmission and is a crucial part of the cruise control. That would be the likely point of trouble if you just had the transmission replaced. Everything I wrote in parenthesis about the flashes was my interpretations and I can no longer alter the post, wheel speed sensors don't affect cruise control operation but a vehicle speed sensor would.
The cruise control servo sits at the back of the engine and is fairly protected, shouldn't have been affected unless somebody were reckless changing the transmission.
Do the self diagnostic and see what you get from it.
Check the switches attached to the brake pedal, and clutch pedal if you have a manual trans. Those switches commonly pop off sometimes for no apparent reason. I have seen it numerous times, so it is just something easy and quick to check.