450SL with odd center dash controls

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
What you describe sounds like the standard layout for a 1974 USA 450SL. The cruise control was made by Philco and that IS the on-off switch. The A/C knob that is broken turns the temperature control for the evap sensor.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.