98 W210 No power to third brake light?

[83w126]

I recently noticed that the third brake like in my E300D was not working, and also did not work with a new bulb. I checked if there was power to the connections where they clip to the car underneath the light assembly and there was not. Unfortunately, that was the extent of my skill at electrical diagnosis. It is far beyond my skill to troubleshoot problems like this and track down the cause, but I have often had good luck with checking things that have failed on other peoples cars. Does anyone have any suggestions?