You have a tachometer that messures rpms?? are a tech/hour meter to messure rideing time? If it is the tech/hour meter and only has one wire comeing out of it than that must be the pos wire and the bracket that u use to mount the meter should be your ground connection. You want to either tap the pos wire into the ignition wire that way whenever the key is turn the meter will come on are if you cant find that wire than run a toggel switch there is a nice location under the front fenders to mount toggels and are easy to get to. Reply back let us know what you have esactly a brand would help and someone will tell you what wire to tap into are i will after you tell me what you esactly have.