How do I connect fuel sender to speedometer

[54Hornet]

Hello,
I have a 2004 130 hp Yamaha, new to me.
The boat came with Yamaha digital tach and speedometer.
Both work fine, except the fuel tank doesn't show on the speedometer,,,the boat has a seperate fuel guage.
On yesterdays outing the fuel guage started acting weird. I filled the tank before leaving, but sometimes the guage was on empty of bouncing around.
Ok, probably needs a new sending unit in the tank.

My questions:

A) Why wouldn't the fuel tank have been hooked up to the digital?
B) To do so, do I just take the wires off the analog guage and hook to the white and black off the speedometer?

I really hate not knowing how much fuel I have.

[rodbolt17]

AFTER making sure the sender is good, yes move the sender wire to the white digital speed and the black to digital speedometer ground.

be aware on the digital fuel, it may take up to 5 minutes to get a change in display if your moving the sender manually.

[54Hornet]

AFTER making sure the sender is good,,,,,,

Further researching on this suggested that people prefer the old style gauges claiming the Yamaha gauge clicks off in 25 gallon increments.
I have a 40 gallon tank,, that would be one click then empty!

I am very interested in getting a flow meter to hook up to the Yamaha gauge.
That sounds much more accurate than either of the other choices.


Thoughts?