I had a problem on a brake light recently. Got a warning, brake light was out, then a wee bit down the road it went away and the light worked again. The next day it happened again - in daylight I could see that the filament was not blown but it had come loose from the pin holding it in place, so it was intermittently touching and working, then over a bump and it stopped working. Replaced the bulb and the warning light was still on... Had to bugger about quite a bit to get the holder back in correctly, even though it felt like it was secured and in properly.