I hear ya..

For those reading, the basic blower control is simply a motor [ power fed by that notorious fuse link] with a regulator on the ground side that controls the speed..the switching transistor in that regulator needs a variable signal from the CP to work..That is the yellow wire.
So, a blower circuit has a simple, 3 step , sequenced test procedure.
Test #1:
Check Red @ motor for 12v..if NO, fuse link is suspect. If Yes, go to test 2
Test # 2:
Ground jumper Blu wire from motor to ground. High fan should result..if Yes, go to test 3..if NO ,blower motor is bad [ brushes/bearings ,etc]
Test #3
With CP on Defrost and Key ON, check yellow wire for Variable V , 2-9v --if Yes, reg is bad, If NO, CP is suspect.

What Benz was nice enough to do was there is a 3 prong plug up top
on most models that have the 3 feed wires [ R/Blk/Yl] , so you do not even have to go to the motor/reg to do the diagnostic power test...they can be tested right at that plug. [ Red/12+..Blk 12 -..Yl/ Var V.+ ]
A Tech would never go down into the blower compartment until he took readings at the top side plug.
It's all in the Archieves,,,,,,,,,,,,,,,,,

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A Dalton