short circuit on trailer light wiring
You have a poor or no ground between the vehicle and trailer.
Brake pedal switch, wiring, bulbs, bad trailer harness (if there), fuses...
Start with: Check fuses, brake light switch (at brake pedal), check for trailer harness problems, check bulbs.
changed brake light switch at pedal and still no brake lights
When you push the brake pedal.
Make sure both bulbs are good (dual filament bulbs) check the brake light switch on the brake pedal. Also, if you are wired for a trailer hitch, the 4-5 wire module may be bad. Eliminate it and check the brake lights again.
Under the brake pedal is a brake light switch that when you press the pedal it hits it and makes your lights come on..sometimes when they get weak the pedal depresses them simply from the weight of the pedal and they stay on..Have a friend get inside the truck and pull UP on the brake pedal as you look at the lights..if the brake lights go off when they pull up on it..then it is that switch under the brake pedal
Check the brake light switch on the brake pedal
When you step on the brake pedal, you close a switch at the top of the arm that holds the pedal. That puts power to the brake lights
manualy lift brake pedal to see if they go out. if so check spring at pedal
check the brake pedal, there is a switch on the back of the pedal that depressed when the brake is depressed that turns the lights on, when this is loose it keeps the lights on.
Brake lights are on continuously while you are driving. Every time the brake pedal is depressed.