A push button switch at the top of the brake pedal arm operates the brake light on a 1994 Chevy 1500 truck. This switch is only responsible for power to the brake lights. The ground side of the brake light socket is grounded at the frame. Most problems arise from either corrosion on the light socket, bad grounds, defective bulbs or problems with the switch or its adjustment.
Check the brake light fuse in the fuse block under the dash on the driver's side. Replace as necessary and retry.
Diagnose the brake light switch with the voltmeter by connecting the voltmeter's black lead to a good ground. Use the red lead to probe both wires at the connector on the switch. There should be battery voltage at one wire. There should be no voltage on the opposite wire until the brake pedal is depressed. When the pedal is depressed, the button on the switch can extend, making a closed circuit. If no voltage is displayed on the wire opposite the battery wire when the pedal is depressed, the switch is bad.
Open the tailgate and remove the screws securing the taillight lens to the body. Pull the lens out. Remove the taillight/brake light bulb and look for a burnt filament. Replace as necessary.
Depress the brake pedal either with a helper or with the use of an object that can be inserted between the seat and the brake pedal to wedge the pedal down. Check the bulb socket with the voltmeter by connecting the voltmeter's black lead to a good ground. Insert the voltmeter probe in the socket with the intention of touching the bottom terminal of the socket only. Try not to touch the side of the socket in the process. The side is the ground and if the bottom, which is the positive terminal, is shorted to the side it will blow the fuse. There should be 12 volts displayed, which means the wiring is good. If there is no voltage being displayed, check the wiring from the switch to the socket.
Release the brake pedal. Place the voltmeter on the Ohms scale. Keep the black lead on a good ground and probe the side of the socket. The display on the ohmmeter should indicate zero resistance to ground. If the display indicates resistance, follow the wire to its ground. Clean and tighten the ground connection and retry.
Install a new bulb and twist it slightly in both directions. If it fails to light, replace the socket because the spring contacts are bent, corroded or worn.
