Digital Multifunctional Speedometer

Upon startup, I discovered that my digital multifunctional speedometer,fuel guage is blank. I have checked power supply and fuses and everything is okay, all other guages are working fine. How do I check if guage is functioning or do I replace guage. My outboard is a 1999 225HP saltwater series.

[boats.net]

If there is 12 volts between yellow and black wire at gauge(with key on) then it should power up, if not probably bad gauge.