Multi function speedometer

[omniboat]

Hi,
I have a 1993 Grady White with a 1993 Yamaha 250. The multifunction speedometer and fuel gauge stopped working. The display shows nothing. The trim and tach display work, but the tach does not show RPM. Is there a trouble shooting guide and wire diagram that I can follow to determine if it is a faulty gauge or bad wiring?
Thanks

[boats.net]

Should have battery voltage between red wire and black wire at speedo, should have battery voltage between yellow and black wires to all gauges when key is on.