Brent,
I am a little confused about your problem. You say that you have a problem with the left brake light. But you don't really define what your problem is. Does it not work at all sometimes, is it dim sometimes, does it stay on sometimes? You say that the lamp warning light comes on because of the left brake light.
So, we can help you more if we know exactly what your problem is.
If the right brake light works all the time, then the brake light switch is good. There is only one circuit in the switch for brake lights and it serves the same signal to both lights.
Another question which may seem unrelated, does the cruise control work?

Together, we can fix this problem.

PaulM

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84 500 SEL (307,xxx miles)