When hooking up a tachometer where do hook the wire to the coil on the left or the right of the coil on a 91 Chevy silverado?

On a 1991 Chevy Silverado, you should connect the tachometer wire to the negative terminal of the ignition coil, which is typically the terminal on the left side when you're facing the engine. This terminal sends the pulse signal required for the tachometer to function correctly. Always ensure that the vehicle is off and properly grounded before making any connections to avoid electrical issues.