After spending a short while wondering why some people were flashing me on the M3, despite my clearly having my headlights on, I realised that my back lights weren't working quite so well. I ended up completing the journey with my foglights on, which only annoyed people marginally less, so I'd love some advice as to what might be causing the problem. I know the rear foglights and indicators work, and the brakelights as well. I have reasonable practical skills, but cars are not my area of expertise, so if you can offer any advice, location and access on the relevant part would also be helpful.
Cheers,
Tom