97- 740I blower motor final stage unit problems

Sorry to post again on same problem but I have done a lot of
electrical work and never had a problem like this car has given me!

blower motor is good and no fuse blows if motor disconnect. Ohms
tested wiring, wiring good. I guess my question is then have any of
you guys seen a brand new from the dealer sealed in box final stage/
resistor unit bad also a used one, both bench tested fine outside of
vehicle the first time? after running the motor and final stage unit
in the car and going back to bench test it blows the circuit breaker
on the testing device also. anyone seen anything like this before?
What solved your problem?

thanks in advance!!!!