TOPIC: Tachometer wiring question

Have two different tachometers, one is an airguide 3fj and the other is an aqua meter. Both have +/- terminals on their backs. I want to install one of these on my 100hp Johnson meteor. The motor is a '67 that was converted from CDI to dist/point/coil. With the new ignition setup should I be drawing pulse from the coil like the schematic shows? Don't know where the gray wire is coming from since the conversion, I'll have to check.