Continuing Ed now says there is one wire from the SAM to each bulb.

SAM is signal acquisition module. These cars aren’t wired point-to-point, rather through networked modules. IIRC the 211 has 3 major SAMs. You or the ambient light sensor decide to turn on the tail lights and the relevant SAMs convene to decide whether to execute.

SDS is star diagnostic system, MB’s service device. Bootleg software and multiplexers and a laptop to make it work is about $800 turnkey from China. There’s a steep learning curve but lots of US support for the asking.

The Autel AP200 is a highly rated by MB forums for working on these cars. There’s quite a learning curve but it’s ‘only’ $70 and works with Android or iOS. You can pay a lot more for not as comprehensive a scanner.

Agreed, a malfunctioning tail light isn’t reason to dismiss a prospect but make sure it’s not the warning sign of an electrical nightmare.

Sixto
05 E320 wagon 212K miles