When I was replacing my blower motor regulator a few months ago, I was curious as to whether one could reinstall the motor backwards. On mine, it was impossible because of the way the cages are designed on each end. It would not fit backwards because one cage was closer to the motor than the other. Of course, like mbdoc said, it is possible to have the wires swapped around and it wouldn't surprise me if some aftermarket part had the colored wires incorrect.

Could your regulator simply be going bad and that is the reason you are not getting the air flow you should? I was having that problem with mine and I originally thought it was the blower motor. I changed the regulator and ended up keeping the same motor, but the flow increased with the new regulator.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles