I bought a used 17" bass boat with a 115 evinrude motor. I need to change the prop on it. It's got a 12-1/2 x 21 sst. My hole shot sucks really bad. To figure out what prop I need, I got to fix my tachometer so I can see how my rpm I'm turning wide open. Does anybody have a clue on how to wire a boat tach. Mine doesn't work and I have no idea which wires to check on the motor. Somewhere between the tach and the motor they change colors so I can't trace them. Any help would be appreciated.