Here's some info from the service manual:
08 - Electrical/8L - Lamps and Lighting/Lamps/Lighting - Exterior/Diagnosis and Testing
LAMPS/LIGHTING - EXTERIOR
WARNING: To avoid serious or fatal injury on vehicles equipped with airbags, disable the Supplemental Restraint System (SRS) before attempting any steering wheel, steering column, airbag, seat belt tensioner, impact sensor or instrument panel component diagnosis or service. Disconnect and isolate the battery negative (ground) cable, then wait two minutes for the system capacitor to discharge before performing further diagnosis or service. This is the only sure way to disable the SRS. Failure to take the proper precautions could result in accidental airbag deployment.
NOTE: When diagnosing the exterior lighting circuits, remember that high generator output can burn out bulbs rapidly and repeatedly; and, that dim or flickering bulbs can be caused by low generator output or poor battery condition. If one of these symptoms is a problem on the vehicle, be certain to diagnose the battery and charging system, then repair as necessary.
NOTE: A good ground is necessary for proper lighting operation. If a lighting problem is being diagnosed that involves multiple symptoms, systems, or components, the problem can often be traced to a loose, corroded, or open ground.
The lamps and the hard wired circuits between components related to the exterior lighting system may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin-out information and location views for the various wire harness connectors, splices and grounds.
However, conventional diagnostic methods will not prove conclusive in the diagnosis of the exterior lighting system or the electronic controls or communication between modules and other devices that provide some features of the exterior lighting system. The most reliable, efficient, and accurate means to diagnose the exterior lighting system or the electronic controls and communication related to exterior lighting system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.
BRAKE LAMP DOES NOT ILLUMINATE
POSSIBLE CAUSE / CORRECTION
1. Ineffective or missing bulb. 1. Test and replace brake lamp bulb if required.
2. Ineffective ground circuit. 2. Test and repair open brake lamp ground circuit if required.
3. Ineffective fuse. 3. Test and replace the fuse in the TIPM if required.
4. Ineffective feed circuit. 4. Test and repair open brake lamp switch output circuit or stop lamp output circuit if required.
5. Ineffective switch. 5. Test and replace brake lamp switch if required.
6. Ineffective TIPM inputs or outputs. 6. Use a diagnostic scan tool to test the TIPM inputs and outputs. Refer to the appropriate diagnostic information.