Drivers side front turn lamp always on

This is most likely a short in the front SAM module.

The front SAM module is basically the lighting control module that is responsible for taking the different inputs from switches and things, and then it sends the voltage to the lamp.

The way to prove this is to check voltage coming into the SAM module from the lamp switch with it off and make sure you have no voltage coming from it.

Here is a guide that will help with this:

https://www.2carpros.com/articles/how-to-check-wiring

However, this is very unlikely because if the switch was the issue then it would not be just one light that is affected.

So for it to only be one light this would be more of a control module issue.

So if it were me, I would unplug the connector and make sure the wires are not shorted to power and then replace the SAM.

Please let me know if you have questions.

Thanks

Hello,

The best way to test a SAM module is to use a scanner that has Mercedes Benz star diagnostics. It will connect to the SAM can tell you if it is good or bad.
When a SAM module goes bad, it usually will have a short or corroded circuit board.

You can typically do a visual check for any corrosion or burnt circuit in the SAM.
A SAM module can be repaired buy replacing shorted/corroded components.

There are few places that you can even send the SAM to be rebuilt.

Let me know of any questions.

Thanks.