When asking for technical help at the very least let us know the version of firmware you are running.Cliff's Calibration (Mapping) Guide is a MUST READ: http://www.vemssupport.com/forum/index.php/topic,97.0.html
It is vr sensor. Third wire is shild. Red wire is -, black wire is +.
take measurements of the resistances across the pins. Pin3 will be the sheild so it will give no reading across the other pins.
It's matter. If you connect opposite you couldn't read rpm.1pin +2pin -3pin shild