Tailights Fade when Braking

[Atl_240sx]

This may seem "overlookable" to some but for me it's kinda annoying. Whenever I'm stopping my car with the park or head lights on, the tailights brighten up on the outer area as normal but the bulbs near the middle fades out completly, yet with the lights off, they come on all the way. I've replaced all the bulbs and the wires seem to be in tact so could anyone help me by telling me how to possobly rememdy this annoying problem?Thanks