Yamaha Tach

[ahill]

I posted this a while back. My Port tach quit functioning. Digital readout is faint to not visible. RPM is not correct Two error arrows show, one heat one oil.
It was sugeted that I check my ground for the tach. My slip neighbor said to put one lead of my multi tester on the tach ground and the other lead to a known good ground. If voltage registers then there is a ground problem on the faulty tach. He also said that a bad ground will backfeed current to a diode in the tach causing the diode to gradually fail.
I tested my grounds and no voltage registered. Any suggestions?
One thing I noticed was that when the ground to the fuel gauge was disconnected and one lead was touched to the disconnected ground from the gauge the meter registered 5+ volts. When the gauge ground was reconnected to the main ground the voltage read 0.0V. I cleaned my two tank sender connections at the tank end first.
not being an electrical wizard, I'm confused by all this.

 

[seasick]

I don't know what the fuel senders have to do with the tachs.
It sounds like the battery feed to the unit is bad or the gauge is bad.

When you turn on the ignition ( don't start the motor), the gauge should go through a self test. All segements should display clearly. Does this happen? If so, the display itself is good.
Does the probelm happen all the time?
If so, it should happen when you power it up as mentioned above.

Check the 12v power connection to the gauge. Even if the signals were bad ( revs, oil, etc) the display should not fade.

 

[ahill]

Fuel sender was just another question.
The tach does not go through self test. With ignition key turned on motor not running the tach goes thru normal alarm mode but the display is faint with an unreadable number on the left side of rpm display. Arrows appear above the temp & oil warning icons although no alarms sound. Same display with motor running although tach readout fluctuates in random nos.
Battery connections are clean & tight. The wiring harness that attaches to the tach lead indicates no grounding issues. The ground from ignition switch to tach also shows as good. This is the second tach for the port engine. Maybe it was weak to begin with.

 

[seasick]

Looks like the gauge is faulty,
One way to check would be to swap the two gauges and see if the problem moves. If it does, the gauge is most likely bad.