Fuel gauge circuit in a boat

[oldcarnut]

I'm trying to sort out a mess of wiring in the boat and have it mostly completed but the fuel level gauge isn't working and I'm not sure if its the gauge or the way it was wired up.  Basically there are 2 wires from each tank.  1ea to grd and the 1ea to a 3 pos toggle switch.  One gauge reads for both tanks depending on which side the switch is on.   The gauge has the center pos switch wire, a grd, and a pos.  Does this look correct?  I filled one side full but no movement on the gauge so I thought I'd ask before digging deeper.

[elacruze]

Where is the gauge in your circuit? What are you using for ground?

[oldcarnut]

The gauge is the circle.  Ground is routed to battery.  Rectangle is 3 position toggle.  Its how it was wired (maybe not right) before I started.  I dont know if it was working then or not.  My father had a lot of loose ends and splices all over in it and Im just trying to get it right

[Tilar]

Are there actually 3 wires going into your gauge? Looks to me like what it "should be, is the hot should go into the gauge like you have it, the wires from each of the two tanks go to the two outside terminals on the 3 position toggle and the center wire on the toggle go back to the gauge. That way you can switch it depending on which tank you are drawing from. The tanks should have a wire going to ground. (by the way I'm seeing it)  Or is that maybe a ground wire on the gauge also?

The way your picture is showing, I would think the gauge would read full all the time.

On the other hand, looking at that pic again you might have the wires on the tanks backwards. Are the red lines on the outside actually wires running from the switch to the tanks?

[2Gunz]

I dont understand your drawing at all.

Generally a fuel gauge works by "closing" or "opening" ground.

I made a drawing for you of how it could be done.  But remember there are many different ways to do this.

Also make sure you dont somehow dead short your tank and make some sparks in or near it.

Also here is something that might be useful.

http://auto.howstuffworks.com/fuel-gauge1.htm

[2Gunz]

Oh and the arrow in the switch on my drawing represents which contact is closed.

So in the drawing you would be seeing the level of the lower tank.

[oldcarnut]

Thanks for the better drawing  .  It's actually showing the same in a better way only the gauge has a ground on it too.  There is a spot on the back of the gauge for grd, send, and +.  All 3 grounds (tanks & gauge)  are connected to the battery ground wire. The toggle is wired the same as yours.  Maybe the gauge is bad 

[elacruze]

It appears to be wired correctly. I'd start by bypassing the switch, simply jumping the sending unit input wire to either of the switch output wires to see if the switch is bad. You should also be able to move the gauge by alternatively shorting and opening the sending unit post on the gauge to ground.

[oldcarnut]

I took one of the sending units out and ohm'd it out.  It looks like both tanks have bad senders so I ordered 2 new ones and a gauge today.  Thanks everyone for their inputs 

[Mytur Binsdirti]

[Tilar]

http://upload.wikimedia.org/wikipedia/commons/thumb/9/96/IGCC_diagram.svg/1000px-IGCC_diagram.svg.png

Flux Capacitor?

[flyinlow]

But where does the beer come out?

[2Gunz]

Looks like a coal fired generator.