There are all sorts of variations with regard to interior illumination in the 300-SEL that are controlled by a switch that's just above the rear view mirror. I'd experiment with the settings and see if you can recover what's missing.
The fuse box is under the hood on the drivers side up towards the firewall. This car uses ceramic style fuses that aren't always available at all parts houses. Over on the Ritter-Easley list, there's a following who believe that ALL fuses should be changed out from time to time whether they appear to be working or not. Sometimes these ceramic fuses appear to be intact, but are not seated correctly.
The slow running fan may be indicative of worn brushes or quite possibly, the cars battery is starting to grow old.
Love those 300-SELs !!!
1991 300-SEL - Model 126
M103 - SOHC
James Madison - Oppressors can tyrannize only when they achieve a standing army, an enslaved press, and a disarmed populace.
Liberty Firearms Training - After years of trying to regulate California criminals with a never ending stream of gun control laws they have still not given up with the belief that if they make something a crime that criminals will miraculously start obeying the law.