I'd love to find the Mercedes engineer who came up with this wiring and ask his rationale for controlling things in this manner. I'm finding more and more that electrical items in cars are interconnected and/or computer controlled seemingly because engineers CAN do it, not because the SHOULD or is logical to do it.
Bottomline, I guess, is just don't check the obvious. The seat controls and lights are so interconnected that even seemingly totally unrelated issues can stem from a common source.
Well be careful what you wish for
A) either more wires going everywhere, and the possibility of fixing your self.
B) All the new stuff with is power, ground, CAN-High, and CAN-low. Plus serialized to the car, and one needs "lock and key license" to buy the sensors/modules/switches. Meaning one cannot buy the part, but one has to have the part put in by a licensed shop with this "lock n key license".
The days of "buying aftermarket"/used/ for all the new cars is over as Mercedes is the one "cornering sales and service". What sold for $50 to $100 for a sensor is $500 from Mercedes plus installation labor...
All the knock, temperature sensors, CPS, and etc are SCN coded like ECU's.
Oh that tranny, limp mode on the electronic tranny(722.6) in a late W140 is like $500 USD(the part in the USA is about $100 to $200 aftermarket) or so. Limp on the 722.9 is like $1500 for the part, and another $1000 in labor or so, and Mercedes does NOT sell this part to any shop(They must have this Lock n Key license), and you cannot buy it either, so the MB dealer in most cases has to do the work as it needs to be programmed to your vin, and the drive software to the transmission must be downloaded to the $1500 part from the Mercedes site. Depending on the year of car the new $1500 plate may not work to the existing valve body on your car, so about another $1000 for a new valve body.
Got to pay to play-yea baby...
Enjoy your old cars because the new stuff is really disposable, or use-it until the warranty expires.