Fuel guage problem

[thebassn8tr]

Let me start off by saying that I have a yamaha 4 stroke 40hp F40TLRY. My fuel guage is not working. When I turn the key, the guage moves. It is constantly reading empty. I know it is getting power. BUT the weirdest thing is that when I turn the navigation lights on, the guage shows "full." Any ideas? BTW, I have no knowledge about outboards but I don't mind getting greasy. Pics would be great but any advice is appreciated. Thanks in advance.

[gonzo]

Reading your other parallel posts, it seems like there is a wiring problem. Probably a bad ground. However, it would be easier for you to find a solution if you posted all the problems together.

[thebassn8tr]

Originally Posted by gonzo

Reading your other parallel posts, it seems like there is a wiring problem. Probably a bad ground. However, it would be easier for you to find a solution if you posted all the problems together.

I did not want to post them all together because I feel that they are un related. The RPM gauge works fine and it is utilizing the same ground.

[tom28571]

The problems may not be related but I'd guess the odds are about the same as winning the lottery against it.

[Frosty]

To explain this properly. If you had a sore throat, runny nose and a headache would you think them to be all unrelated? or one problem affecting all?

[stonebreaker]

I agree with Gonzo, you have a wiring problem. The fuel gauge is really an ohmmeter, it reads resistance. The float in the gas tank varies the resistance, but the problem is loose connections can also cause the resistance to vary, which screws up the calibration of the gauge. Make sure all your wiring is tight and not corroded.

[Frosty]

Yeah but he has also sited a thread about his trim guage not working properly. He has also said that his navigation lights affect the fuel guage.

Every body is correct here.

What is very likely is a ground ( i think some one said that) this means that voltage if unable to go the ground (back to neg) will oppose other voltages meaning no flow of current wich will do all sorts of magical things.

Because a wire is connected does not mean it is electricaly connected, even a bunch of wires can have some in contact and some not . A dry or coroded ( absalute typical in marine enviornment) groung wire is suspect.

[thebassn8tr]

Thanks for the info. I guess that I should just take it to the basics and trace every wire and it's connections.

[thebassn8tr]

One (probably no brainer) question that I have about the fuel gauge is that I only see two wires coming from the gas tank (one pink and one black). Shouldn't there be at least a third one for the sending unit coming out of the tank?

[Frosty]

No -2 wires is all thats required. For a fuel guage you will have a supply from the ign sw this goes to the guage then to the sender then to ground-- check the ground. It will be shared by others remove and clean thouroughly.

This circuitry is also exact as the temp and oil pressure. They are merely votage guages. The senders ( bieng different for each) are directly affected by fuel content ,temp or oil presure, accordingly.