2006 Toyota Sienna brake indicator problem

1.the brake light (indicator) on the dashboard is off  when I use the brake, it just won't turn on. 

2.when accelerating or turning, the brake indicator sometimes is on and in about 10 seconds it will be off.

 

I will take the car to shop tomorrow. I appreciate any suggestions on the problem.

 

BTW, the brake fluid is full and the brakes work very well even when the indicator is off.

 

Thanks