Hi All, replying my own question.
due to inaccurate nummbering of the B-connector on a certain website, there was confusion regarding pin 7 and 8.
depending on what site you start with number 1 .

so the yellow-black on B is the SPEED PULSE wire.
for any other who gets confused too.

Hi,

did the upgrade from the SC805 to the SC901 in my 97 V90.
incredible sound !
can you tell me the function of the yellow/black wire to the B-connector of the 901
it connects to pin 8, the so called non-connected pin.

my 901 seems to work fine without this wire connected.

thanks for your replay.