is it the abs or e brake light? More than likely it is an abs sensor. cost about 50 bucks to have replaced on my car hope this helps. If it is the red brake light, there is low fluid or the e-brake pedal is sagging. Check the reservior and top it. If it is the orange brake light, you'll need to have the ABS system tested to determine the cause. Or you could blindly buy and install parts as a guess.
There should be a bracket mounted on the steering column near the floor. This will have a switch in it that is a plunger type. When the shaft of the brake pedal is depressed, it comes into contact with this plunger and activates the brake light circuit. If you "ride the brakes", your brake lights will always be on because of the minimal pressure required to activate this circuit.
If both brake light bulbs fail to come on when the brake is depressed I'd check first to see if there may be a fuse that controls the brake light circuit. If there is no fuse and/or the fuse appears to be okay, the most likely culprit is a faulty brake light switch. This switch is located up and behind the brake pedal. There is a plunger that moves in and out acting as a switch when the brake pedal is depressed. It is this switch which possibly may be the culprit.
Your Brake light is a warning light, it means something is wrong with your brakes, first you should check your pads for wear (if you feel a grinding sound every time you press the brakes they are shot), sometimes brake pads have wear indicators (a wire that when the pad wears surfaces closing a circuit and turning the light on), another possibility is low brake fluid level. Another yet is that one of the circuits has failed (there are two), If all these checks do not give you an answer, take it to a specialized brake shop, you don´t want to suffer the failure of your brakes when least expected, NEVER save mone on brakes, they are the most important system in your car.