Just for fun....
That picture is in Andrew Noakes' "Mercedes SL Series The complete Story". It is on page 88. There is another picture of the same interior on page 91 that is little better picture of the switches on the left of the steering column. Still hard to determine what they, or it, is. My guess would be some type of auxiliary light switch. The second picture also clearly shows the car is finished in a flat color which, to me, indicates it may have been an early production car used for development purposes.
Norm