Hello, I am John, a Ford dealer technician.
I hope I can help solve your problem quickly and accruately.
There is a common problem that could be affecting your truck. It could be the cruise control deactivator switch. This could be in two places depending on the options your truck has. Either it is on the master cylinder directly behind the reservoir or it is on a bracket behind the brake pedal. If it is on the pedal it will have a black plunger that moves when you touch the pedal. Either of these is most likely the cause and they are both under $30
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If it was the brake pedal switch wouldn't that affect the brake lights as not to work? My brake lights do go on and off when using the brakes.
The switch on the master cylinder - can I do an ohms check on the switch or is it work or don't work.