This connection has nothing to do with the aquabus. It is just for the PWM control and RPM monitoring.
It might be possible that the aquabus interface port on your controller board is damaged.
With a multimeter that has diode testing capabilities you can easily check that yourself.
Please check the attached photo:
aquabus_test.jpg
The following test must be performed while the pump is not connected at all.
Set your multimeter to the diode testing icon that I have marked with red circles. Put the black ground tip to the first pin of the aquabus port and the red voltage tip to the second pin of the aquabus port. If the aquabus port is OK you will get a reading of about 1,9 volt. Repeat this measurement with +/- in reverse.
Some cheaper multimeter might only show "OL" (overload) or something like that to tell you that the measured value is too high for the device. Well, you can still consider it as OK in this case.
A reading with a voltage below 1,0 volt indicates a damage of the aquabus interface.