Thanks a33b, see the attached. Why do you think disabling 0500 would be dangerous? Sending the signal to the ECM might be difficult as it must come thought the CAN line from some other module (ABS or TCM, I dunno) and the Nav doesn't have either, although the gauge cluster can send out a speed signal to the old diesel ECM. Anyway I may have bypassed the problem temporarily by shorting the neutral position switch so happy days, for now

. Also, have you ever modified the PWM signal for the tacho?