Brake light switch

Stop Lamp Switch Replacement
Removal Procedure
For information on stoplamp circuit diagnosis, refer to Lighting Systems in Body and Chassis; and Electrical Diagnosis.

Caution: Unless directed otherwise, the ignition and start switch must be in the OFF or LOCK position, and all electrical loads must be OFF before servicing any electrical component. Disconnect the negative battery cable to prevent an electrical spark should a tool or equipment come in contact with an exposed electrical terminal. Failure to follow these precautions may result in personal injury and/or damage to the vehicle or its components.

For Vehicles equipped with OnStar  (UE1) with Back Up Battery:

The Back Up Battery is a redundant power supply to allow limited OnStar  functionality in the event of a main vehicle battery power disruption to the VCIM (OnStar  module). Do not disconnect the main vehicle battery or remove the OnStar  fuse with the ignition key in any position other than OFF. Retained accessory power (RAP) should be allowed to time out or be disabled (simply opening the driver door should disable RAP) before disconnecting power. Disconnecting power to the OnStar  module in any way while the ignition is On or with RAP activated may cause activation of the OnStar  Back-Up Battery (BUB) system and will discharge and permanently damage the back-up battery. Once the Back-Up Battery is activated it will stay on until it has completely discharged. The BUB is not rechargeable and once activated the BUB must be replaced.

Disconnect the battery negative cable.
Disable the SIR. Refer to Disabling the SIR System .

Remove the pushrod retainer from the brake pedal pin. Use snap ring pliers.
Unsnap the stoplamp switch from the pushrod.
Disconnect the electrical connector from the stoplamp switch.
Installation Procedure

Connect the electrical connector to the stoplamp switch.
Snap the stoplamp switch onto the pushrod.
Install a new pushrod retainer on the brake pedal pin. Use an 11 mm (7/16 in) socket in order to push a new clip onto the pin.
Connect the negative battery cable.
Enable the SIR. Refer to Enabling the SIR System in Supplemental Inflatable Restraints.

If I remember correctly you can unlock it with a screwdriver from the side on the passenger side of the shifter. Sometimes you have to take the console off though. Look next to the shifter if it's on the console. If you see a little piece of plastic and it will say park release. It will look like a little bump. Pop that up and stick a screwdriver straight down and you should be able to release it from park. Otherwise you'll have to take the console apart.

It's behind the steering column. Twist it and it comes out. The stop light extension harness has a little metal bar on it. Push this down and the switch pops right off.

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? Stoplight switch is mounted on top of brake pedal

Okay, all research I have found looks like you will need to remove the lower underside panel of column in order to gain access to switch.

Not entire dash, no. Should just remove panel that is above brake pedal to gain access. Usually contains 4 - 6 bolts in panel.

Have assistant press brake pedal and check for twelve volts at brake light socket.

These are easy to trace, locations (such as a relays/ fuses, etc.) are listed beside them.

It might be easier to begin with the lights (bottom diagram) work your way through the system sort of backwards, as starting at the top might lead you around like a maze!

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

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