When you say "3.0", are you referring to a MaruLabs BEP 3.0?
If the answer to that question is "yes", then you pick up the signal for the Koso speedometer from the SPD output on the BEP. That output will go to the speedo input on the Koso. The black ground wire from the Koso will go to ground on the bike and the remaining wire you just ignore (because is normally is used to provide power to the Koso sensor).