Like the title of the thread says, no power to the third brake light. Where do I start tracking this down? I checked under-hood fuse and there wasn't anything for a third brake light, same with the door-jamb fuse box (that one did have some sort of brake light fuse, but it wasn't blown). The regular tail brake lights work.

I removed the fixture and tested for voltage at the terminals that the wires plug into; reading was zero.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280