Before replacing the brake light switch on a Chevy or other vehicle, first check to ensure that the problem is with the switch itself. Check the fuse that controls the switch, and look at the wiring to make sure it's intact. Open the driver's door fully, and remove the mat to make the switch as easy to reach as possible.
Brake light switches are difficult to access, but using a fairly strong light can get a better view. The switches are generally far up along the pedal on the inside of the dash board cover. Remove the cover at the bottom of the dash panel that's over the switch, using a screwdriver to do so if necessary. After snapping off the cover, use a socket wrench to remove the bolts holding the switch in place. Detach the electrical connector to shut off power to the brake lights and to prevents shocks.
Attach the electrical connector to the new switch, and bolt it into place. Screw the cover back into place. Test the brake switch by making sure the brake lights come on when they're supposed to and stay off when the pedal is not depressed. Adjust the locknut to ensure proper operation.