Hello, I have a 2010 C300 4M Sport with about 275K on it and towards the end of last winter I notice that whenever the temperature was below freezing my lights would dim and brighten on a 3-4 second cycle. It was more noticeable if the car was running above 1500 rpms. I checked it on a volt meter, at the battery, and sure enough it would cycle between 11v and 14v .. but again only when the air temp was below freezing.

At first I thought battery since the one installed was pushing 5 years old, so I replaced it and it still occurs.

I was wondering if it’s possible that some sensor was involved…maybe with a bad relay…? Are there any sensors that are activated at 32/0 f/c?

I did have the alternator replaced the previous summer but there was a period of time earlier in the winter when I did not have the problem, so that would think not, but I guess some bad electronics within the alternator is also a real possibility. So the next question would be, is the regulator part of the alternator in this car? and would a regulator fail in such a temp senstive way?

Open to any thoughts and opinions,

Thanks,

Dave
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