if you were concerned about tapping into the ABS system you could use a separate ABS sensor on one of the wheels. you would need to make a mount for it, should not be awfully difficult. then you will need some circuitry that will determine if the sensor is picking up movement in the wheel or not. then send that signal to your switching device for the vents. there is also a hall sender in the speedo cluster that may be of use for the same purpose of sensing road speed.

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punkinfair