One problem related to brake light on has been reported for the 2012 Mazda CX9. The most recently reported issues are listed below.
Brakes prematurely failed after feeling numb and squishy. Upon diagnostic by a local mechanic, it was determined that the brake master cylinder had a leak. In addition, the abs, traction control and emergency brake lights came on when the symptoms were present. Estimated cost of repair $1250.