digital tach

Hello-I have recently acquired a used 1988 precision blend 130 hp. Starts and runs well-good compression etc. The tach doesn't work. I have connected the like color wires as is shown in the seloc manual I have just purchased. The manual refers to a connection inside the remote control box. I have lights on the tach but no RPM readout. There was one schematic which said to connect the blue to the yellow wire to bypass the light switch. haven't been able to find those wires. Any ideas? Am I heading down the right path?

[boats.net]

The green wire at 703 control box or ignition switch panel is the tach signal wire, make sure it is connected and tach is set for 12 pole alternator.