How to Wire a Motorcycle Tachometer | It Still Runs Loosen a bolt near the engine, such as a hardware-mounting bolt or cylinder-head bolt. Set the end of the ground wire underneath the head of the bolt. Tighten the bolt down on top of the wire to keep it in place. Start the motorcycle and watch the tachometer. I installed an aftermarket tach on my motorcycle. I ran Green wire on tach to signal wire. Red wire to hot wire with ignition on. I had to use a single-fire adapter to this tach as it is for dual-fire and my bike is single-fire with two coils.