2005 Silverado Brake Lights
 

I have a 2005 Silverado. The right rear brake light is dimmer then the left when the running lights are not on. While the running lights are on the right rear brake light goes completely out. I replaced the circuit baord mounted to the frame and it didn't change anything. Have replaced the right brake light socket. I have traced the wiring back under the bed as far as I can see them and found no damage or corision. Has anyone else had this issue and if so what was done to fix it?