There isn't a single, dedicated relay for power locks on a 1999 Chevy Silverado 1500. The power lock system's operation is typically controlled by the Body Control Module (BCM) and uses several circuits within the BCM, rather than relying on a separate relay. The BCM itself is the central control unit, and any problems are usually traced back to it or its related wiring.
Therefore, you won't find a relay specifically labeled "power locks." If you're experiencing power lock issues, you'll need to troubleshoot the system starting with the BCM, fuses, and associated wiring. A scan tool capable of communicating with the BCM would be beneficial in diagnosing the problem.
