Fuel gauge stuck past full

blackbuck350

Apprentice
May 2, 2019
71
8
Today I went out to start the wagon been sitting up about 2wks I noticed when it was running the fuel gauge had went way pa full and now it’s stuck there, any idea what’s going on has new sending unit thanks
 
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g0thiac

G-Body Guru
Sep 6, 2020
753
63
Today I went out to start the wagon been sitting up about 2wks I noticed when it was running the fuel gauge had went way pa full and now it’s stuck there, any idea what’s going on has new sending unit thanks
Wiring for the sender unit to the dash is old and need replacing.

If it’s past full, check the tan (or whatever color yours is) wire behind the instrument panels or that the plug is in there ok.

Do not worry about grounds either, I know first hand from fixing my my fuel gauge, that it goes BELOW empty if that was the issue.

Most likely, you will need to run new wiring from the tank to the dash like I did unless its clear, where the wire is broken and repair that area lmao.
 

melloelky

Comic Book Super Hero
Oct 22, 2017
3,766
113
mass
check the ground from the sender to the chassis,if that's bad it pegs beyond full.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,814
113
If the ground is bad, or the gauge wire is broken, bad contact, etc., you'll get a past full reading every time.

Couple of things I may suggest:

Not an electrician, but I've seen this before. Had to fix this before, too. It sucks worse when you're old, but get your butt under the gas tank and search for two things coming from the top of the tank, a wire that's grounded to the body somewhere and a wire that goes to the gauge, which should have a rubber boot connector on it. Check immediate surroundings there for any breaks in the wires. Check your ground wire to make sure it's got a good ground. If you have to remove the little bolt and clean the terminal, do that. Then recheck your gauge.

If still past full, pull the connector apart on the other wire, check to make sure the terminals are clean and in good shape. Ground the wire from the gauge and then check fuel gauge. If it doesn't go to empty, then you either have one of two things- bad wire back to the tank (as mentioned previously) or the sender is fooked. It could even be the ground where it attaches to the sender.

The gauge wire connects via the pin on top of the sender, and a pass through connector, and then there's a push nut holding the wiring to the sender parts. You can access it only by yanking the sender from the tank because it's underneath the sender cover plate. The push nut works loose sometimes and causes the connection to become loose there. If it's tight and in good shape, then the sender itself is probably hosed, and you'll need to get a new one. Ensure any replacement matches the piping of your original, either 2 port or 3 port.

Obviously there's good ways of using a meter to check all the resistance, etc., on all the wiring, but basically, there's two components that could go bad, the fuel gauge or the tank sender. Everything else is just wiring.

images
 
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airboatgreg

Comic Book Super Hero
Oct 2, 2016
2,735
113
Disconnect the sensor wire and see what the gauge does. Use a test light with one end to ground and the other to the wire to the dash at the sender with the sender disconnected. Let me know what you find
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,300
113
Galaxy far far away
Bad ground will peg the needle past full. Low voltage is full, high voltage is empty. At least the fuel gauge isn't computer controlled like on new cars.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,814
113
when the pink wire going to the fuel gauge is grounded, the gauge goes to empty
Gauge seems to be good. Now to figure out if your ground wire has a good ground, and the connection to the sender (usually a round push on connector) is nice and tight. Pull the pink wire sender connection off and ground it if you haven't already and make sure the entire wire is still good.

Tank still accessible to take the sender out? You can take out the sender, hook it up to the pink wire, then ground it, and play with the level float and see if the gauge swings. May rule out the sender at least.
 

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