The windmill is connected to the battery, through the blocking diode.
The windmill does not connect to the dump load.
The dump load connects to the battery.
No current will flow through the windmill until after cut in RPM is reached.
You are shorting the windmill with the dump load.
I do not know what kind of controller you have, but if the instructions recommend this type of testing, then the controller will not result in a good outcome.
G-