GMC Repair: brake sender on a 1999 Chev silverado, keyless entry system, back of the cab

Question
1999 Chev Silverado
The brake lights do not come on when the brake pedal is pushed but do the lights do have power to them and work with the keyless entry system.  I was wondering what the brake sender? would cost and if this is my problem.  The strange thing is that the brake lights on the back of the cab work with the brake but not the lights on the back of the truck.

Thank you

Brett

Answer
I would check the bulbs first because they have 2 filaments, one for park lights and one for brakes.

After that if the third brake lamp works, but the rear ones do not it is porbably your Multi-function switch, also known as your blinker, cruise, and wiper switch.