To test the brake light switch, raise your eyes under the dashboard, and find it up the top of the brake pedal and unplug the electrical connector. To check continuity, connect an ohmmeter to terminals of the switch and to find that there is continuity between terminals A and B when the brake pedal is depressed and no continuity when the pedal is released. In case the switch does not work in the desired manner, then you ought to adjust it, or otherwise change it. To adjust, take out the electrical connector of the brake light switch and loosen the locknut and turn the switch until it makes contact with the pedal and turn it another 1/2-turn and then tighten the locknut. To replace, disconnect the electrical connector, loosen the locknut and take out the switch with the installation being the opposite of the removal with a need to adjust the switch later.