If one brake light isn't working the problem is probably a bulb that needs replacing. If both brake lights aren't working it is probably the fuse or the switch. Pull the fuse to the brake lights and replace it if it is blown.
If it is not blown get to the switch. Most cars have the switch located somewhere on the brake pedal. It generally has a plunger that is moved when the pedal is depressed. Unplug the switch ( with the key in the off position ) and use an ohm meter to test for continuity when the switch is in the position it would be in if the brake pedal was depressed. It should show continuity or open circuit ( in most cars ) in that position. If it is not malfunctioning see if it gets fully depressed when you push the brake pedal. If not adjust it so it does. If this doesn't work you have a short in a wire somewhere.
If it is malfunctioning, or if you don't have an ohm meter, take the switch out of the car, take it inside and carefully take it apart. Don't forget how it goes back together! Clean the parts inside that are metal ( probably copper ) of any corrosion and reassemble it. If this doesn't work you will have to buy a new switch.
replace the break light bulbs?
brakelight switch, it is located under the steering column, and above the brake pedal where it connects to the car there is a little plunger switch up there.
check the brake light relay under the hood
usually faulty brake lights are either the brake light switch that senses when you press on the brake pedal, a connector somewhere between the brake light switch and the brake lights or the turn signal switch.
The brake lights in your 1983 Nissan pickup truck are controlled by the brake light relay switch. When the brake light relay switch malfunctions the brake lights will stop working.
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.
It depends on the exact problem. If it's that both brake lights in the back do not work and the middle one works, it could be your turn signal switch.
Don't know the year of the truck, but check your brake lights. On year models that you have to press the brake to shift, without a brakelight signal you can't get out of park. Turn the key halfway between lock and on and you can get it out of park.
Adjust or replace the stoplight switch at the upper end of the brake pedal under dash area
Check fuse Check stop light switch - usually located at the upper end of the brake pedal under dash area
check fuses, check brake light switch behind brake pedal.
To fix a 95 Dodge Dakota with no brake lights, first check to ensure the fuse has not blown. If the fuse is good, check to ensure the brake light bulbs are not burn out.