Question Lights that indicate that anti-lock brakes are not working are: Answers Gray. Blue. Yellow. Explanation Vehicles equipped with Anti-Lock Braking Systems (ABS) have yellow malfunction lights to indicate issues in the braking system. Take a FREE Practice Test Now This questions appears in the following tests: Hawaii Knowledge Test Class B , Alabama Double , Washington Double , Idaho Air Brakes , Iowa Air Brakes , Mississippi Air Brakes , Nevada Air Brakes , South Dakota Air Brakes , Virginia Air Brakes ,