504 Fuel Gauge
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Thread: 504 Fuel Gauge

  1. #1
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    Icon6 504 Fuel Gauge

    Trying to get the fuel gauge to be something like accurate. If I disconnect the wire to the sender unit in the boot I get 7.5 volt to earth. What would you expect? Does this indicate a short in the wire somewhere?
    Thanks
    Glenn

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  2. #2
    1000+ Posts Beano's Avatar
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    I don't know what voltage you should expect, but I do know that if you take out the sender you will most likely see wires wound around a flat piece of bakelite, and an arm which travels across them. Those windings tend to bunch up due to the arm pushing them.

    Apart from getting a new one, I've never been sure how to fix this. The arm only just touches the windings, so you don't want to stuff around with it all too much. But I did once entertain the thought of pushing them all back where they should be and trhen super gluing them in place.

    Or getting the same kind of card from another car and hoping the resistance is the same.

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    Quote Originally Posted by Beano View Post
    I don't know what voltage you should expect, but I do know that if you take out the sender you will most likely see wires wound around a flat piece of bakelite, and an arm which travels across them. Those windings tend to bunch up due to the arm pushing them.

    Apart from getting a new one, I've never been sure how to fix this. The arm only just touches the windings, so you don't want to stuff around with it all too much. But I did once entertain the thought of pushing them all back where they should be and trhen super gluing them in place.

    Or getting the same kind of card from another car and hoping the resistance is the same.
    If you get a 504 fuel gauge to be accurate it will be a first and a Nobel prize may come your way!
    Tom_95 likes this.

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    Fellow Frogger! ipb205's Avatar
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    Pics below of a new old stock sender that I have if they are of any use. '12V' is noted on the white plastic section.
    Upon inspection they don't look to be very solid or 'rebuildable' at all. As described by Beano above the arm only just touches the winding or metal strip and the whole thing is very delicate.
    I had a fluctuating gauge in the past and an auto electrician just popped the dash top off and added an earth direct from the back of the gauge to part of the chassis metal nearby and it fixed the issue. Id try that first. Sounds like you have voltage at the rear of the car so it may be at the gauge area.
    This gauge is for an 'Early' car as per the sticker and Im not sure if they changed later on or when.

    504 Fuel Gauge-20180805_093338_resized.jpg
    504 Fuel Gauge-20180805_093349_resized.jpg
    504 Fuel Gauge-20180805_093403_resized.jpg
    Last edited by ipb205; 5th August 2018 at 09:48 AM. Reason: added info

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    My 504 cab had an extra earth wire fitted from the instrument panel when I bought it .Maybe it was for this .The gauge never shows completely full or empty but goes from three quarters to one quarter and I use the trip meter to know when its time to fill up.

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    the electricals inside the sender is just like a variable resistor, due to years of movement the coil winding would have had massive wear and carbon built up, so first bet is to replace the sender, second ensure your ground is good. I would always reground various section of my car back to the battery negative points. lots of improvements especially for the electrically related parts.

    With the wire unplug, the supply to my 404 sender is something like 10.5 volts.

  7. #7
    1000+ Posts Beano's Avatar
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    The grounding idea sounds good. There is only one wire going to the sender and the tank may not be earthed well anymore....7.5 volts seems low.

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    Adding to my previous post ,I know it reads three quarters when full but I don't know what it reads when empty because I never let it get anywhere near empty .All I know is the gauge goes down as fuel is used.

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    Does any one know if there is a difference between an "early" and a late, 1978, 504 fuel gauge sender?

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    Hi lpb205

    I have tried to find out if there is a difference between early and late models without success. If you want to part with this sender I am interested. Price? Send me a pm if you like. Thanks Glenn

  11. #11
    1000+ Posts Peter Chisholm's Avatar
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    I'm pretty sure my 1980 504 has a sender (same as 505?) which is different to early 504. Not sure about 1978 504.

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    Thanks Peter but that indicates the one above may not be an option. Glenn

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