If your brake lights are not working properly, here are the first three things that you should check out. It is important that you do this right away, as driving without working brake lights is unsafe for you and the drivers that you share the road with.
#1 Brake Light Bulb
The first thing that you should check is the brake light bulb. If your brake light bulb is burned out, then all you need to do is replace it. You can tell if the brake light is burned out if the wires inside look black or grey instead of clear or white; it is the same as checking and seeing if any other light in your home is burned out. If you suspect that the brake light is burned out, purchase a new one at your local auto parts store and replace it.
The access to your brake lights may be set up one of two ways. In older vehicles, you typically have to remove the panel covering your brake lights and the screws holding it in place to access your brake lights. In newer vehicles, there is generally a panel in the corner of your trunk that you have to remove to access the brake lights.
#2 Brake Light Socket
The second thing you need to check is the socket that holds your brake light in place. If the socket looks a little rusty, you are going to want to wipe the socket down with some white vinegar to remove the rust that has developed and see if your lights now work. If the socket is extremely rusted out, you'll want to have your mechanic replace it.
#3 Fuse Box
Third, a switch may have been flipped on your vehicle. If your brake lights are not burned out and the socket is in good condition, this is the next thing that you should check. Generally, the fuse box is located under the dashboard; however, check your owner's manual for specific instructions on how to access the fuse box on your particular vehicle as the location and ways of access can vary greatly from one vehicle to the next.
Once you have gained access to the fuse box, you should see numerous wires connected to one small black box. These wires are connected to all the lights in your vehicle. Inspect these wires and see if any of these wires has split or broke or look like it has become burned or frayed. If you spot any wires like this, you are going to need to replace all of the damaged wires. Your owner's manual should help you identify which colored wire is connected to which lights, including your brake light.
If you want, you can purchase replacement fuses from your local auto parts store. You will need to remove the old wire and put the new wire, or fuse, into place. This is a relatively simple job but if you don't feel comfortable doing this, your mechanic, such as Gordie's, should be able to do this job for you in under an hour.