I also experienced this problem where both bulbs worked until I reassembled the dome light into the position, then the left light was either dimmer or did not work at all. After several removal and replacement attempts I found that as RED RUNNER (no relation that I know of) suggested, the bulb socket was not fully rotated and seated. Play with it until you are SURE it is inserted correctly and has been rotated a quarter turn to the lock position. All should be well . . .