Wire colors? (most helpful in identifying things)(photo arrived while writing this: white with red stripe)
((second intense stare showed a lengthwise green stripe)) ... so it's either DG/WT/RD or WT/DG/RD in MB-speak.
Which country are you in?
2003 (close enough) US
service manual, wiring diagrams (but not "S44" type numbering) are section 8W.
There are "connector pin-out" pages showing the shapes and wire colors of the connectors.
Given the colors ... give me a couple of minutes to dig a bit...
(the brown is "ground")
added: by the 2003 service manual, it doesn't
appear to be speakers.
My memory from another search is that the "S44" is a switch connector designation.
So it could be a rare instance of something in the harness for an option you don't have.
It's also very rare for there to be a switch without the additional wiring for illumination of the switch.
added after more digging: if what i'm seeing as "white" is really "gray" (thus GY/DG/RD), it could be the lighting circuit to the security system's Panic Alarm switch. (page 8w-39-7 of the 2003 service manual).
..but lacking the additional two wires for the Panic button itself.
Ahhh... GY/DG/RD is the general "light the switches (and lights)" circuit ... the same colors (and only 2 wires) and pin assignments (it looks like 1 and 3?) go to the ash tray lamp.
--dick