New fuel gauge and sender but gauge peggs to full

xagneovox

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Feb 3, 2017
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36
Hello,

Recently I bought a new fuel gauge and sender.
In the shop they told me that the gauge and sender are good to use with each other with the resistance.

When I tested the sender, connected to the gauge it worked like it should.
Now installed when I turn my key the fuel gauge peggs over full.
I think it's a problem with my ground connection.

My gauge has 3 connections,
- ignition
- ground
- sender

The ignition is connected to my ignition cable behind the key.
The ground is connected to my ground cable begind the key.
The sender is connected to the center bolt of my fuel sender.

My sender has 2 connections,
- The center bolt is connected to my sender connection on the gauge.
- A bolt on the side connected to my negative ground of my battery.

When I connect the gauge only with my ground and ignition the gauge stays empty so the gauge should be good.
The sender I tested manualy before the installation and it worked also.

Inside the cork washer of the fuel sender is a metal staple to connect my center bolt to my ground, I think this is the problem but I don't know how I should properly connect this if this should be the problem.


Regards,

Jasper
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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verify your sender wire is not pinched and grounded somewhere

verify your gauge sender is sending 240 ohms when empty and 33 ohms when full
 

xagneovox

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36
The sender wire is connected with a ground with a staple that runs trough my cork gasket wich connects to my ground of my sender
 

Silvertip

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If the center bolt on the sender is grounded, that is why the gauge is pegging. The center bolt/stud must NOT be grounded. It is the resistance element of the sender. If it is grounded there is zero resistance and hence, the full reading. There should be no connection other than the pink send wire on the sender stud. There is a situation where you may have overtightened the send wire on the stud and turned the stud. This can short the internal connection of the stud to the resistance element.
 

xagneovox

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Ok that's what I thought, but how can I ground my sender without making connection with my center bolt? I'll uploade a picture in a minute
 

xagneovox

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I saw that the crimping tube of the sending cable was damaged but it does not touch the grounded bolt, however inside the rubber gasket between the plate and fuel tank has a staple inside for making connection wich the shop owner told me not to remove?
 

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xagneovox

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The pictures are in the 6th post, and already thanks for the fast reply's guys :)
 

Jcris

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I agree with silvertip and scott
That staple is probably for grounding purposes
Did you remove it, or was it damaged on install? Pull the sender and inspect that
 
Last edited:

xagneovox

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No, it was like this built in when I bought, I just removed the sender so the staple does not make connection annymore and it still pegs out, first i tought it was because i took the ground and ignition from my tacho because when i moved my float the tacho went up and down, I tried directly on my fuel gauge so without the tacho between and it's still the same.

When i move my float manualy the guide on my gauge moves but only minimal, I don't think the gauge and sender are not corresponding because I had it working before the installation
 

Silvertip

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Are you certain you have the wiring on the correct terminals? If you took power and ground from the Tach and then the tach responded to the sender, that says you connected the SEND wire from the sender to the tack. And are you looking at the terminals and markings properly. You may be confusing which terminal is which. You keep mentioning that the ground and send terminals are connected to the threaded post on the sender. That is simply not right. There should be one connection and one connection only on the sender post. Thats the wire that runs to the SEND (S) terminal on the fuel gauge. The only other connection at the sender is the metal flange needs to be grounded (negative terminal of the battery). Once more time -- did you check the ribbon connection from the threaded post (under the flange of the sender) to make sure you did not spin it and make contact with the metal shell on the sender. That's a typical failure because people tend to use Herman Munster muscle to tighten the nut and then they end up spinning the stud. I have a hunch you also have the wiring wrong up front. Your fuel gauge should have a fourth connection (one for the internal light) and it would be labeled "L".
 

xagneovox

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Silvertip, that's what I also tought so I switched the cables but it didnt work. I don't umderstand what you mean with the ribbon connection but I shal make a drawing of the cables and post it so you van see how my cables run and yes there is also a fourth conmection for the light boulb but it's not connected yet
 

xagneovox

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No Title

So the first problem of the pegging shall be the staple that connects the ground of my fuel tank to the sender so it gets infinitive ground amd peggs, this I understand now.

The positive pole and ground are connected to the ignition switch but it's the cabling imside my commander unit made by omc and I don't know how they are connected so I didn't draw them for not to confuse you :).

Is this the right way to put the cables? If so I can check for other problems.

Regards, jasper
 

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Bondo

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Ayuh,... Fuel tank ground actually goes to the motor's block, which is grounded to the battery,...

So, Ya, both pictures are right,...
 

Silvertip

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On your diagram, why is the SENDER cable going in two directions? It should go one direction only and that is directly to the "S" terminal on the fuel gauge. It should not go to 12V or ground or to any other point. Switching cables is not a diagnostic approach. You need to know which cable you are dealing with at all times. Just because you removed it the threaded stud on the sender does not mean it is actually the SENDER wire. The ribbon I mention is under what connects the threaded stud on the sender to the resistance element on the sender. You cannot see that unless you remove the sender. If you over-tighten the sender wire nut you can spin the stud slightly which twists that bare ribbon wire to the point where it touches metal. That grounds the "S" terminal on the gauge and the gauge pegs full. If you had a VOM you could disconnect the sender wire and check resistance from the stud to the flange. If you measure something between 30 and 240 ohms that short is not the problem. If it measures closed circuit this is definitely the issue. Here is a link to picture of a sender that may or may not be identical to yours. http://www.ebay.com/itm/Marine-Boat...ng-Unit-12-to-24-Deep-Gas-Tanks-/162052369556. Note the wire running from the resistance element at the end of the support to the stud at the top. Some senders have a flat piece of ribbon-like wire that connects to the stud. Again, if that stud spins, the uninsulated ribbon wire can contact the metal support and short the sender to ground, thus pegging the gauge.
 

xagneovox

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Silvertip, thank you fornthe good explanation, I just found the problem, the ground I used for the gauge was not good, I tried with a direct ground to the battery and it worked so with an other cable and other ground it works like a charm :)

Regards, jasper
 
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