Over the past 9-10 months I've had several people stop me and let me know my left rear brake light was out. Each time after checking on it myself later at home, I never found a problem.

Finally, after my buddy followed me back to the office from lunch one day and he said it was out the whole way, I decided to just go ahead and replace it.

No more than a couple hours after replacing it, I had someone pull up next to me at a light and alert me that it was out again. At this point I'm about to lose my mind so I did some experimenting.

Turns out, when my lights are on, the brake light works fine. When my lights are off, the left rear light doesn't work at all. Hence why I never saw a problem since I always checked at night with the lights on.

Any ideas what could be causing this? I'm assuming it's a short somewhere but don't really want to deal with the $$$ of getting that fixed.

Thoughts?

I would make 100% sure that the bulb you installed is the exact same as the one on your other taillight.

The original bulb could have had an intermittent problem making contact then loosing contact and that would be issue 1.

The new bulb, if purchased somewhere other than a Toyota dealer can have offset pins or connections which can give you this issue as well.