I just got a w140,early model,1992,with a dead blower motor.I grounded the blower directly and it works,full speed,so,I assume regulator is faulty.The one on the car is a Behr,I dont know if that was the factory model,before I spend 100$+ for another one,is there anything else worth checking?ACC seems working,I can hear switching vents when I push the buttons also it will turn the AC compressor on if set on defrost...

I'd stick with the behr. Use the Buy Parts link here on the forum - they've got a good price and it helps support this wonderful site.

I have a '92 300SE as well - and I've been "through" that car from nose to tail (bonnet to boot?). Don't hesitate to PM me with questions when they come up.

Regards.

Grounding the motors neg. side simply means you have taken the switched ground control circuit out of the system. [ by-passed]
So , you MAY have a bad regulator, but you could also have no variable trigger voltage to the regulator. The regulator has to have a trigger signal in order to complete the blower ground circuit. No trigger sig =no blower.
You want to check the 3 wire connector at the firewall , behind the brake booster. You need var/voltage at yellow wire for the reg to work.
The wires there are rd/blk/yl.
r to blk-12v
y to blk- var 2-8 volts , depending on speed selection.
If no var voltage at yellow, then the problem is upstream from that connector, not downstream/regulator...

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A Dalton