There should be a grey wire in the cable leading to the control or dash, whichever. That grey wire is the tach signal wire. There should also be a black wire, probably grounding the control. The black wire is also used as the ground wire for the tach. Wire gauge really isn't all that important. Set your tach to 6 pulses (12 poles).
If your tach is illluminated, the light wires connect to the boat's running lights.
