Pressure Differential Warning Light Switch

Attach a bleeder hose to bleeder valve at either rear brake. Immerse other end of hose in container with brake fluid. Turn ignition on.
Open bleeder valve while pressure is being applied to brake pedal. Warning light should activate. Close bleeder valve before pressure is released from pedal.
Reapply brake pedal using moderate to heavy pressure. Light should go out. Repeat test on front brake system. System should function in same manner. Turn ignition off.
If light does not operate as specified for either system but comes on when electrical circuit is tested, warning light switch portion of valve is defective.