My left brake light wont work on my 2000 C280. Searching for electrical help.

Not a lot of information there to respond to. But first meter the brake light terminal to see if you're getting 12 volts to it while depressing the brake pedal. Another thing is to verify that you are using the CORRECT BULB type for your car. Another thing is not to use LED bulb, i.e. test with the designed filament bulb of the correct type. Another thing is to look at the fuse map for your model and check the continuity of your brake light fuse. that is just for starters

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-- raymond~
47º 34'N 122º 18'W

Did you check the bulb? Go take the bulb out and swap it over to the right side. Put the right side bulb into the left side. If the problem is now on the right side, you have your answer

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1990 190E 3.0L

Inspect the tail light bulb holder,the tabs for the bulbs can wear loose