Your brakes lights stay on not all the time what do you do.it is a Chevy truck 2002?

Under the brake pedal is a brake light switch that when you press the pedal it hits it and makes your lights come on..sometimes when they get weak the pedal depresses them simply from the weight of the pedal and they stay on..Have a friend get inside the truck and pull UP on the brake pedal as you look at the lights..if the brake lights go off when they pull up on it..then it is that switch under the brake pedal