I just bought my 16 year old son a truck. 1993 F150 xl supercab. 302v8 with 3speed automatic and overdrive. The truck was well maintained and in great shape. A few minor issues, but we're fixing everything up. Today, we went for a ride and found that the cruise control does not turn off when you apply brakes. Fortunately, he just turned it off via the button on the steering wheel.
I looked around. There is no de-activation switch on the master cylinder. The brake lights are working. It got late so I didn't get under the dash yet. Is the brake light switch a dual switch? A normally open for the brake lights and a normally closed for the cruise shut-off? All other electrical systems seem to be working ok.
Any help is appreciated.

 

brake lights turn off the cruise.
but if the brake light switch is out of adjustment, the brakes can be applied without the lights coming on/cruise turned off.
i had that happen a few times on my trucks
you would have to really step on the pedal to turn the brake lights on.
readjust the brake light switch and everything was back the way it should be.

 

The brake lights work properly. Only problem is cruise control not turning off.

 

do the brake lights come on when resting your foot on the pedal, or do you have to step on it?

on mine the lights would not come on until you STEPPED on the pedal.
this of course would cause the situation you have, the brakes would apply, but the cruise would not turn off.
once the switch is properly adjusted, the cruise now turned off and hte brake lights came on when as soon as your foot touches the pedal.

 

Is this a factory system or aftermarket curse control?

Sounds like you have the older vacuum control cruse control unit as you do not have the master cylinder switch(if factory). Verify as its a big round servo. While checking the brake light switch, also check the vacuum dump valve. Its located off the brake pedal bracket and has a vacuum hose attached to it. To adjust it, just turn the lock nut loose and turn the valve so when the brake pedal as at the rest stop, it press up to hold vacuum. As soon as you press the brake pedal, it should dump the vacuum.

Now if you have the electronic factory cruise system, or aftermarket, then it's a electrical. Most likely the brake switch wore out.

 

It sounds like someone has left out the auto transmission clutch jumper or the Brake Pressure Switch is bad. You may also have a bad Brake Off On (BOO) switch.
You have the electronic speed control without any vacuum hoses or fitting.
By the way it is call Speed Control on a Ford and not curse control on this era of truck.

How The Circuit Works:

The Speed Control Servo/Amplifier Assembly controls vacuum to move the throttle through the Actuator cable.

To operate the Speed Control System, the engine must be running and vehicle speed must be greater than 30 mph. The System is turned on by pressing the Speed Control Switch ON.

Pressing and releasing SET/ACCEL or COAST sends a command to the Speed Control Amplifier. This command makes the vehicle's current speed the set speed. The Programmable Speedometer/Odometer Module (located in the Instrument Cluster) sends a speed signal to the input of the Speed Control Servo/Amplifier Assembly through the 679 (GY/BK) wire. This signal tells the Amplifier to increase or decrease the throttle to keep the vehicle at the set speed.

Pressing and holding SET/ACCEL increases the vehicle's speed as long as SET/ACCEL is depressed. Releasing SET/ACCEL gives the System a new set speed to maintain. Vehicle speed may also be increased by depressing the accelerator until the higher speed is reached, then depressing and releasing SET/ACCEL.

Pressing and holding COAST decreases the vehicle's speed as long as COAST is depressed. Releasing COAST gives the system a new set speed to maintain.

Pressing OFF turns off the System (grounds LB/BK wire). The System is also turned off when the Ignition Switch is turned OFF. Depressing the brake pedal cancels the speed controls. The Deactivator Switch also operates when the brake pedal is depressed. This is a backup device that releases the servo. In vehicles with manual transaxle, the Clutch Switch opens when the clutch pedal is depressed and cancels the System.

When the System has been cancelled by depressing the brake or clutch pedal, the last set speed may be resumed by pressing RESUME. This feature will not work if OFF has been depressed or with car speed below 30 mph.



The above is assuming the OP's truck has factory installed speed control. /

 

The Brake Pressure Switch is located near the RABS hydraulic module along the driver side frame rail on a 1993 model year F-series truck. I have owned two of them...

Also assuming the OP's truck has factory installed speed control.

 

That was it. Thank you.

 

I have the same problem on my '88 F-350 but I believe it's a vacuum system...