Rear light problem

Hi,

My light bulb warning light came last week so after a quick investigation i replaced the drivers side rear brake light bulb. Tonight when i started the car up the warning light came on again. Its the same bulb again. I took the bulb out and it looked fine but i thought i'd buy another bulb and try that. The warning light has gone off but the light doesn't seem to be on. It comes on when the brake is applied. I removed the lamp holder and the bulb is lit, just, but its very dim.

Has anyone else had this problem? Its not the bulb as i've tried several, what can it be?

Thanks, Lee