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.