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12roadking
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118 Posts
Discussion Starter #1
hey everyone,so I put in a new Harley speedo/tach. gauge and flush mount gas caps.the gas gauge doesn't work unless I plug in the original gas gauge also,can something be jumped in the harness for the original gauge??just don't like the look of the original gauge,thanks for any help
 

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Just Ride
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3,255 Posts
Maybe new gauge is bad
 

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Retired citizen
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23,364 Posts
As a test apply B+ to the new gauge to see if it pins out. Make sure you use the correct color code wire and it needs ground too.
 

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12roadking
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118 Posts
Discussion Starter #4
the new gauge works if the old gauge is plugged in???just wanted to delete old gauge completely
 

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Registered
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39,492 Posts
What is the part number of the new fuel gauge?

Is the new fuel gauge part of the speedometer, or the flush mount gas cap?


There is a voltage divider circuit in the stock gauge that is needed to complete the circuit similar to the one shown below. That is why the gauge on the speedo wont work with the original removed.






With the original gauge removed, there isn't even anything hooked up to the float. And thus nothing is getting a reading off it.


You could simulate a fuel gauge being there by connecting a correct resistor between the yellow and black wire where the original fuel gauge plugs into, and another resistor between the yellow and orange wire. But I wouldn't know what the correct resistance values are without dissecting a working fuel gauge.
 

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12roadking
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118 Posts
Discussion Starter #6
will post it after work not sure till I get home thank you
 

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12roadking
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118 Posts
Discussion Starter #7
The new gauge part# is 70900072A,the fuel gauge is part of the Speedo not the cap.thanks again for the help and info. I really appreciate it.
 

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12roadking
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118 Posts
Discussion Starter #8
So I'm going to dismantle the factory gauge and try mounting the insides to the bottom of my new flush mount cap.Will post the outcome this weekend
 

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12roadking
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118 Posts
Discussion Starter #9
so I was able to disassemble the factory fuel gauge and drop the circuit board down in the tank hole with a piece of truck camper foam strip and put my flush mount cap over it and all works aok.i called my local dealer to see if there was anything plug in to replace it and he sounded pretty confused?,and hasn't got back to me yet.
 

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Retired citizen
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23,364 Posts
That piece of foam is down inside the tank ???
The gas will eat that foam up and it might plug the fuel filter and injectors or carb passages.
I'd get that foam out of there soon.
 

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Registered
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39,492 Posts
That piece of foam is down inside the tank ???
The gas will eat that foam up and it might plug the fuel filter and injectors or carb passages.
I'd get that foam out of there soon.
He's talking where the phony gas cap/fuel gauge goes.

No fuel in that area.
 

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Retired citizen
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23,364 Posts
Okay, I got it.
That new gauge the OP has sounds like a H-D part number, I'm surprised it's not plug n play !
 

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Registered
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Okay, I got it.
That new gauge the OP has sounds like a H-D part number, I'm surprised it's not plug n play !
It is, BUT the fuel gauge in the speedo depends on the original (or replacement) fuel gauge to complete the circuit.

He does not want a fuel gauge in the left cap.

What is the part number of the new fuel gauge?

Is the new fuel gauge part of the speedometer, or the flush mount gas cap?


There is a voltage divider circuit in the stock gauge that is needed to complete the circuit similar to the one shown below. That is why the gauge on the speedo wont work with the original removed.






With the original gauge removed, there isn't even anything hooked up to the float. And thus nothing is getting a reading off it.


You could simulate a fuel gauge being there by connecting a correct resistor between the yellow and black wire where the original fuel gauge plugs into, and another resistor between the yellow and orange wire. But I wouldn't know what the correct resistance values are without dissecting a working fuel gauge.
 

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12roadking
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118 Posts
Discussion Starter #14
Exactly and the original gauge has to be able to move for the resistance change or the new gauge won't read correctly,strange.
 
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