The tach signal wire runs all the way to the back of the cluster. When we installed a tach in my bro's 91 crx we just tapped into the tach signal wire behind the cluster. I cant remember what color the wire was behind the cluster though. If i recall correctly it wasn't a blue wire behind the cluster so it changes color somewhere between the dizzy and cluster. A wiring diagram would help you figure out what wire is for the tach signal behind the cluster.