Whoops! me bad. I looked at the wrong side of the harness in the S/M. The correct connector (on the back of the radio ) is M43 pin 9. It is te sky blue wire. And yes it is an input signal to the head unit. Vehicle speed is not sent to the head unit over CAN. I design amplifiers for a supplier to Nissan and I have designed around this function in several applications. See page AV-15 and AV-18 in the S/M.