There is a connector on the motor that provides the grounds to illuminate lights within a conventional Yamaha tachometer or icons within a Yamaha multifunction tachometer. Those grounds could be wired to a relay that would then power a much brighter light at the helm.
A relay so that current...
The -50-00 wire harness will not work with the later ECU's.
Would be very simple to wire a bright red light on the dash to indicate the nature of the warning alarms. One for temperature. One for oil pressure.
Or to wire in a larger warning horn.
Now with a problem resulting in the warning...
The black wire, the green wire and the yellow wire will give you RPM information on the tachometer.
Other wires are used to for the oil status lights. I don't think that vintage tachometer has an over temperature light.
The tachometer and its lights are unrelated to the warning horn. That is, the horn will sound and the motor will go into RPM reduction mode even if there is no tachometer installed.
What type of Yamaha control box do you have?
That is the Mercury serial number. You can go to the Mercury Marine website and insert that number into a search box. It will take you to the parts catalog for the motor.
The ECU is monitoring engine temperature. If and when the motor gets too hot the ECU will sound the alarm and put the motor into RPM reduction mode. The Command Link gauge will indicate the problem.
Is it all that important that the NMEA 2000 display indicate some particular temperature value?
