Check all fuses.
Wait until dark.
Park where you could see the glow of the brake lights from inside the truck, were they to illuminate.
Press and hold the brake pedal.
Wiggle the turn signal switch about for a few seconds. If this causes the brake lights to work or to flicker, replace turn signal switch.
Move tilt steering up and down. If this causes the brake lights to work or to flicker, replace turn signal switch.
Switch 4-way flash hazard lights on and off a few times. See if that does anything interesting.
Check for Body codes.
the switch on brake pedal is faulty and needs replacing
It is probably the brake lights that are on due to a misinstalled or damaged brake light switch.
If your brakes lights are not working and all of your other lights are OK try replacing your "brake stop switch". You may have to have either your local auto shop or local dealer replace the switch because it's hard to do yourself. I had the same problem on my Tahoe and replacing the brake stop switch solved it right away.
Your fuse could be blown, or the brake light switch is improperly adjusted.
The switch on your brake pedal that controls the lights is most likely stuck, try some WD40 before replacing it.
Defective or out of adjustment brake light switch, if the switch is mounted on the brake lever. If the switch is on the master cylinder, then it needs replacing.
On most vehicles pressing the brake pedal activates a brake light switch which is usually located near the brake pedal. It will be this switch that is faulty. Replacing it is probably the best option.
Brake light switch needs adjusting or replacing. It is too sensitive.
It is because the brake light switch under the brake pedal is faulty. usually replacing this will solve the problem. it is designed in such a way that when the brake pedal is depressed the switch completes a circuit and the lights come on. the fault occurs when the switch closes the circuit even though the pedal is not depressed. hope this helps.
Common issue...if the brake light swith is not working; the cruise control will not engage and your brake lights will not go on. replacing switch is easy and inexpensive...its located in the upper part of the brake pedal.
If the brake light fuse is good then it can be the brake light switch. Some are mechanical switches and some are pressure switches. If it is a pressure switch, the switch will be on or near the master cylinder, and you will see a wire going to that switch. If it is mechanical, the switch will be located somewhere on the brake pedal swing arm. it may just need adjustment or it may be bad and need replacing.
Check to see if you have knocked the brake light switch off of its mount. It is located above the brake pedal.