Brake Light Bulb: Description and Operation

The brake system indicator light comes ON to alert the driver that the parking brake is applied, or that the brake fluid level is low. It also comes ON as a bulb test when the engine is cranked.

Bulb Check
With the ignition switch in ON (II) and the engine not running, the alternator applies a ground signal to the WHT/BLU wire to turn ON the brake system indicator light as a bulb check.