Try cleaning all the connections on the rear bulb holder. I was having issues with my rears, when I pressed the brake the indicator bulb on the dash would come on slightly, and if I had the indicator on and braked the indicator went off. Also sometimes if I had my lights on the rear wouldnt be on.
I took the holder off, cleaned up all the connections and it works fine. And that was a good 2 months ago and no problems since.