Its above the brake lever, underneath the dash. First, push the brake pedal down and watch the switch to see if the button comes out, it could just be gettin stuck. If it looks fine, take out the switch or just unplug it and if you have an ohmmeter check the switch out. It should read low ohms with the button out, and high ohms with it pushed in. If it reads high both ways the switch is bad.
If you dont have an ohmmeter you may wanna pickup a new switch, you could always return it. I payed $5.87 for mine.