[JSeery]

Are you saying that you are getting power to the tail light (brake) connector? I'm assuming pos (+) ground? Need to check for power at each point along the circuit starting with the brake switch.
1.) Check for power on the battery side of the brake switch
2.) Check for power on the brake light side of the brake switch and see if it goes on and off with brake application.
3.) Check the next connector down the line between the brake light switch and the brake lights and find where the power is not present (with the brake applied).
There are two ways there can be a problem, a break in the circuit or a short. If power is making it all the way to the brake light socket, then remove the bulb and check the pins in the socket. If there is power to the pins, then there is ether a bulb problem or a ground problem.