sotongalaxy

Hi I have a v reg 2.3 Petrol Galaxy. my brake lights no longer come on when the main lights are off. They do however come on and stay on when the main lights are on??.. push the brake pedal makes no change. I seem to recall replacing the bulbs around 2 months ago and was unsure if I needed dual filiment or single. bought the dual, but all seemed to work fine. I have sprayed the pedal switch with WD.. just not sure what to do from here?. Any help please?. Thanks Rob