The Trailtech TTO tachometer can take it's signal off of the ignition coil primary wire. It is documented in the installation instructions and has worked very well for me. Now that my OEM speedo has died and I'm replacing it with a Vapor, the installation instructions say nothing about this tach signal option, only winding the sense wire around the spark plug wire. Anyone know if i's OK for me to use my existing coil primary signal wire for the Vapor as well? Anyone else use this signal pickup for their Vapor tach input?