I'm almost finished with this boat, and I was gonna buy a OMC tach but I have an AIRGUIDE tachometer that came on the boat where I got the motor from, so I'll goahead and use it. When I tested the motor the tach worked so I am sure it is fine...the question is there is 2 wires on the tach...yellow and black...how are they gonna hook up on the 3 wire harness that comes out of the control box. It's a Johnny '79 100hp motor, TIA<br /> 