All,

I have a 1974 450SL that I'm driving and fixing, fixing and driving.
The center dash controls seem odd, and as I'm trying to install a stereo
system I really need to know what's so with them.  I haven't found a
configuration like this described in any documentation I have.  (I'm
waiting for the service CD from Mercedes; they said they were doing up a
new one, so it would be delayed.)

The layout is like this: on each side, there are the usual up/down
sliders for temp and airflow.  In between, in the left upper quadrant is
a knob to control the blower fan, which works fine.  In the right upper
quadrant is an odd control that is marked for the cruise control; all
the docs I have state the cruise control controls are on the turn signal
arm.  In the right lower quadrant is a knob marked with two speaker
outlines, and since my car has speakers in the dash AND behind the
seats, I assume it's some sort of fader; the car had an original
AM/FM/cassette (in questionable condition).  The left lower quadrant
holds the control that really mystifies me: it's a knob that says "Fresh
Air" above it and "Inside" below it, with a centerline and a zero
character to the left.  The actual knob is broken off, and there is a
bulb in the erstwhile control's shaft.

Does this sound familiar?  Do I have a "grey market" car, or just some
custom control setup?  Or do I just have crappy documentation for 450s?
 I'd be most grateful for any guidance you can offer.  TIA -- Ian