1955 Fuel gauge always past full

[Tori]

My 1955 6 volt positive ground. My fuel sending unit shows over full all the time. When I check the wire hooked to the sending unit it is hot. When I unhook the wire on the sending unit the gauge goes to empty. It’s a new sending unit. How do I check to see where the problem is?

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[dmsfrr]

When you say the wire to the sending unit is 'hot'... do you mean temperature? or it has electrical power on it?

The dash gauge and wire to the tank appear to be working normally. The replacement sensor is not.
The float may be stuck in the up position or it has an electrical problem. The new replacements aren't made the same way as the originals. They aren't always electrically compatible with the original dash gauge, and they are most likely made in china. Their quality isn't that good to begin with.

Are there any other wires connected to the terminals of the sensor for the fuel tank? If there is also an added ground wire connected somewhere that may be the problem?
.

 

[biddle]

@Tori the title/subject of your post should be a summary of what your post is about, which in this case is your fuel tank sending unit. Your subject "1955 6 volt positive ground" has been updated.

 

[74 Harley]

The sending unit is a variable ground. Make sure your wire to the sending unit is isolated and not grounded out.

 

[Pink T-Bird]

My 1955 6 volt positive ground. My fuel sending unit shows over full all the time. When I check the wire hooked to the sending unit it is hot. When I unhook the wire on the sending unit the gauge goes to empty. It’s a new sending unit. How do I check to see where the problem is?

I agree with @dmsfrr that your dash gauge and wiring is working properly if the gauge is full when connected and empty when disconnected at the tank.
Which means your sending unit is either defective, or the float arm is stuck. Pull the sender and confirm the float arm moves freely. If it does, you have a faulty or wrong sender.

 

[Sharecropper]

I went through this same thing with my '56 12 volt system and a Chevrolet truck. In both cases it was the China sending unit.

 

[sylvurhfox]

Tori,
I had the same issue when I put my car back together. I even replaced the sending unit in the tank. I hooked the sending unit up and raised the float by hand and the gauge went down. I lowered the float and the gauge went up. I found the wiring on the gauge was backwards. However I had taken my car completely apart into pieces. I don't know if this will help or not.

 

[dmsfrr]

... I found the wiring on the gauge was backwards. ...

What year car? original or after-market parts? you mentioned replacing the sending unit.
The old style King-Seeley gauges in a '55 Bird work on current flow and heat. They aren't supposed to be voltage or polarity sensitive.

The newer off-shore replacements are made completely differently.

 

[sylvurhfox]

This is in a 1955 Thunderbird 6V positive ground. After switching the wires on the gauge, the gauge worked properly However the fuel level on the gauge goes passed full and it takes about 60 miles before it starts to move. The sender should be adjusted but I am not taking my trunk liner out for that. I will just deal with it.

 

[dmsfrr]

This is in a 1955 Thunderbird 6V positive ground. ... the fuel level on the gauge goes passed full and it takes about 60 miles before it starts to move. ...

That's better than the car I usually drive.
It stays slightly above full for the first 120 miles then goes down from there. And it's a '19 Toyota. Go figure...

 

[Ward 57]

That's better than the car I usually drive.
It stays slightly above full for the first 120 miles then goes down from there. And it's a '19 Toyota. Go figure...

Some cars have odd shaped tanks to fit. I also had a couple of cars where the top end of the tank was much larger than the bottom. Took forever to get the needle to move and the all of a sudden it drops like a rock after the 1/2 full mark.