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Discussion Starter · #1 ·
I'm having an issue with my 05' Springer (fxstsi), for some reason the fuel gauge is giving a false reading of full when the bike is running. However, it does slide down to the empty/red area when the bike is shut off.

-Has anyone ever had this issue? If so is this an easy fix?

Or

-Does anyone have any recommendations on how to correct this issue.

Thanks.
 

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Sounds like it is your fuel sender unit that is out, as your fuel gauge has full movement.


I'll pull up diagnostic info when I get home.


I had to replace the sender unit in my '05 earlier this year, but mine was reading 1/4 tank even when full.
 

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Fuel sender puts out the following resistances between the black and yellow wire to the fuel gauge:

Full 27.5Ω - 39.5Ω
Half 97Ω - 118Ω
Empty 240Ω - 260Ω


If your yellow wire is shorted to ground, it would cause it to read full.

Disconnect the fuel gauge wiring harness from the sender unit under the instrument cluster and measure the resistance of the yellow wire and ground of the harness going back to the gauge. Should read open.
 

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I have the exact same issue on my 04 Fatboy. I haven't started T/S it yet. I assume the resistance readings posted by Kainam are the same on my unit...

Maybe I will wait until you figure out your problem, then I will work on mine.
 

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I have the exact same issue on my 04 Fatboy. I haven't started T/S it yet. I assume the resistance readings posted by Kainam are the same on my unit...
Yep same sender unit was used on 04 and 05 softails.


A constant full reading would be indicative of the insulation on the yellow wire between the sender unit and the gauge being chafed through and shorting to ground.
 

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. . . A constant full reading would be indicative of the insulation on the yellow wire between the sender unit and the gauge being chafed through and shorting to ground.
This . . .

Or failure of the sending unit.

A short to ground would be at or near 0 ohms resistance. The "Full 27.5Ω - 39.5Ω" is because of the nature of the potentiometer in the sending unit. Anything less than that would also equate to full. And of course, the short cause the resistance to never change with the movement of the float.

If you have a DMM, you can test it at the plug at the back of the fuel gauge. Then test it where the wires exit the tank. I'd do it with a half a tank of fuel so you can have some expectation of the reading.

If you have a good resistance reading at the tank exit but not at the gauge, trace the wiring. If it is also bad at the tank exit, you either have a bad sending unit or the short is inside the tank.

Also, the wire that triggers the low fuel light is dependent upon the same send from the sending unit. If it is wired in parallel - which I believe it is - a short there would cause the same issue. You'd have to pull the dash up off the tank to check that. That wire is part of the main speedo cluster.
 

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This . . .

Or failure of the sending unit.

A short to ground would be at or near 0 ohms resistance. The "Full 27.5Ω - 39.5Ω" is because of the nature of the potentiometer in the sending unit. Anything less than that would also equate to full. And of course, the short cause the resistance to never change with the movement of the float.

If you have a DMM, you can test it at the plug at the back of the fuel gauge. Then test it where the wires exit the tank. I'd do it with a half a tank of fuel so you can have some expectation of the reading.

If you have a good resistance reading at the tank exit but not at the gauge, trace the wiring. If it is also bad at the tank exit, you either have a bad sending unit or the short is inside the tank.

Also, the wire that triggers the low fuel light is dependent upon the same send from the sending unit. If it is wired in parallel - which I believe it is - a short there would cause the same issue. You'd have to pull the dash up off the tank to check that. That wire is part of the main speedo cluster.


In my case, the pivot for the float got worn out causing the wiper for the potentiometer to not make good contact with the variable resistor (an open reading when using a multimeter), causing an empty reading (actually 1/4 tank, it was making slight contact) at the gauge at all fuel levels.
 

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I believe I still have my old fuel sender unit that I can take photos of, if that will be of any assistance.
 

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Discussion Starter · #10 ·
Well thanks for the replies. I consider myself pretty handy when it comes to working on my bike but I'm definitely not skilled in the electrical department. Sounds like she will be heading to the shop.
 
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