Fuel gauge wrong reading...
Seasoned HDF Member
Joined: Sep 2008
Posts: 14,157
Likes: 11,247
From: San Diego, CA
I'm asuming a bent float arm because there was some "work" done in the past in the tank. When I was removing gas from the tank I was simuntaleously measuring the resistance and it was dropping smoothly.
I'll measure the resistance at the top position of the float so that I'll lift the float through filler hole and than we'll see. If it will be to low than it is a probably bent arm...
I'll measure the resistance at the top position of the float so that I'll lift the float through filler hole and than we'll see. If it will be to low than it is a probably bent arm...
If the issue appeared right after the "work", then it could be a problem with the float's range of motion..
But if it took awhile for the issue to appear, then range of motion is less likely..
Keep us posted on what you find out...
Good luck with the repair
Seasoned HDF Member
Joined: Mar 2021
Posts: 18,450
Likes: 3,716
From: backwoods
One I had out had contacts the float. I wonder if gently cleaning those would change the resistance.
I don't use it anymore. It is nice to show almost full in case I forgot to reset tripmeter.
I don't use it anymore. It is nice to show almost full in case I forgot to reset tripmeter.
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Cruiser
Joined: Nov 2025
Posts: 180
Likes: 109
From: Slovenia
Ok made some more tests.. The float works ok. I emptied the tank completly and the resistance is 242ohm. If I pull the float all the way up it is 42ohm. If I dissconect the gauge, the light comes on. Then I reconnected the gauge and measured resistance and it was105ohm and the light didn't turn on... I'm a bit confused right now... ..It's not a problem geting out of fuel, I too rely on an oddo...it just anoys me, cause it's not working as it should and I can't figured out why...
Stellar HDF Member
Joined: Sep 2021
Posts: 2,047
Likes: 1,486
From: Black Hills of SD
Did you turn the ignition off and back on at that point? The ECM may need to reset itself after you disconnected the fuel gauge. I am only spit balling here and I do not know what the resistance spec is.
But it does sound like the slider is getting a signal through its range of motion. It just may not be the correct resistance signal, meaning corrosion could still be a factor. I do not know if there is a spec for that in the manual - Have you tried to look that up?
But it does sound like the slider is getting a signal through its range of motion. It just may not be the correct resistance signal, meaning corrosion could still be a factor. I do not know if there is a spec for that in the manual - Have you tried to look that up?
Last edited by MarlinSpike; Apr 14, 2026 at 02:21 PM.
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Cruiser
Joined: Nov 2025
Posts: 180
Likes: 109
From: Slovenia
Sender is in correct range. I checked all connectors and there is no corosion. And with everything pluged the resistance is to low or I'm missing something... by them self all systems works as they should I supose, but when connected together something goes wrong...
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Cruiser
Joined: Nov 2025
Posts: 180
Likes: 109
From: Slovenia
Second, but my 86 Sportster has nothing except oil light🤣.
If contacts get dirty the resistance goes up. In my case the resistance is lowered...or there is something that I don't understand...
If contacts get dirty the resistance goes up. In my case the resistance is lowered...or there is something that I don't understand...
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Seasoned HDF Member
Joined: Sep 2008
Posts: 14,157
Likes: 11,247
From: San Diego, CA
I know what you mean, my OCD makes me crazy when something isn't working like it's supposed to.... 
You report that the sender measures in spec, yet when attached to the gauge, the gauge isn't reacting properly to the signals. Sure sounds like the wires/connectors somewhere between the sending unit & fuel gauge have an issue, or that maybe the gauge itself has an issue.
I have to admit, I am not an electrical guru. I am unsure if the gauge itself interprets the changes in resistance, or the ECM does that and then sends a signal to the gauge... On the carb bikes I believe it's the gauge that does the interpretation, so it's probably the same with the EFI bikes (until the BCM was introduced).
Just some food for thought....
Have you inspected the fuel gauge connector where it plugs into the wire harness at the frame backbone, under the tank? It's not always easy to get to and manipulate with the tank on the frame, but it's doable. Have you inspected the fuel gauge wires that come out of the bottom of the tank to the connector on the harness for signs of chafing?
When you inspect the connectors for corrosion, also inspect the connector pins. They can get bent causing connection issues. Also some of them can become dislodged in the connector housing, causing them to slide back (out) when the connectors are put together, also causing connection issues.
You report that the sender measures in spec, yet when attached to the gauge, the gauge isn't reacting properly to the signals. Sure sounds like the wires/connectors somewhere between the sending unit & fuel gauge have an issue, or that maybe the gauge itself has an issue.
I have to admit, I am not an electrical guru. I am unsure if the gauge itself interprets the changes in resistance, or the ECM does that and then sends a signal to the gauge... On the carb bikes I believe it's the gauge that does the interpretation, so it's probably the same with the EFI bikes (until the BCM was introduced).
Just some food for thought....
Have you inspected the fuel gauge connector where it plugs into the wire harness at the frame backbone, under the tank? It's not always easy to get to and manipulate with the tank on the frame, but it's doable. Have you inspected the fuel gauge wires that come out of the bottom of the tank to the connector on the harness for signs of chafing?
When you inspect the connectors for corrosion, also inspect the connector pins. They can get bent causing connection issues. Also some of them can become dislodged in the connector housing, causing them to slide back (out) when the connectors are put together, also causing connection issues.
Last edited by hattitude; Apr 15, 2026 at 08:42 AM.
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Cruiser
Joined: Nov 2025
Posts: 180
Likes: 109
From: Slovenia
The gauge itself is actualy not that much of if indeed is... I have two gauges which reads pretty the same.. The only connector that wasn't checked is the one on the backbone...that one will have to wait until next winter when the tins are going to respray...so this is it probably for this season...