Wilsons Sandbox

Hello, Lurker here, very much in debt to you all. Fast question: I am wiring in a device which needs to read the tach signal to calibrate to the engine RPM. I tried splicing it into both the + and the - coming off the low-voltage side of the ignition coil under the tank. Neither worked. That's what the tach reads, right? Or is it another wire off of the Ignition Module? Thanks! Michael Z Jersey City/NYC 1999 KLR 650 (x2) 1982 Seca Turbo