whats the year of the engine?? and what tach do you have?? does the engine have a electronic ignition?? if so there should be an electronic box aka CDI or powerpac inside or on the CDI there should be a grey or white wire thats the tach wire, the only real important wires on the tach to get it working is the grey, black and red wires. connect the grey wire of the tach to the tach wire in the outboard connect the red wire to a power source and ground the black wire. I hope this helps it could very well be different with your setup, but thats how it went hooking up a 1999 teleflex tach to my 1994 evinrude motor. good luck