The brake light switch is up underneath near/connected to your brake pedal arm. Also, don't rule out that you simply have a bad bulb or corroded connection possibly causing the issue. If it is a bad bulb, see sources and related links below for bulb information.
The 1991 Volvo brake light relay switch is located beneath the drivers side dashboard. The brake light relay switch will be above the brake pedal.
check the switch at the top of the brake peddle.
Above your left Knee when you are driving
where is brake light switch
Check the bulbs, check the fuse, check the brake light switch, in that order.
Look under the dash on the driver's side, half way down the brake pedal. When you depress the brake pedal, the pedal moves away from this switch, which allows the brake light pedal circuit to complete, and your brake lights come on. This brake light switch is always hot/on, as required by federal law, so that even with no key in the ignition, if you hit your brake pedal, the brake lights will come on.
If you are referring to the warning light on your instrumentation panel, then you simply need to check all your brake lights, do not forget the center one at the rear glass.
You can try to reset your brake light switch by unplugging the brake light switch and plugging it back in. If that does not solve your problem you will need to replace the brake light switch.
a switch that is trigered to light up the light when the brake pad is pushed in
The Chevrolet Colorado brake light switch is quite simple to change. The brake light switch simply plugs in and out.
The brake light is controlled by a relay switch. If the relay switch is bad the brake lights will stay on. The brake light switch simply plugs in and out. Unplug the brake light switch until you can replace it.
Above the brake pedal. If your main brake lights dont work but your third center brake light does, then the brake light switch is not the problem. Its is the turn signal switch.