1967 camaro console

Hello everyone, I'm a young mechanical engineer. I've been working on my 1967 Camaro for about 8 months and am currently in the process of installing a console and gauges in my car. I've been studying the wiring diagram and seeing what the best way to do everything is and I noticed that 1...

I installed the factor tach and bought a new wiring harness. The plug that comes up to the speedometer has a wire coming off of it and I'm not sure if this powers the tach or if the tach is powered through the plug that goes into the speedometer? I've attached a picture. I know that the yelow...