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Discussion Starter #1
Hi all,

My fuel gauge - after some intermittent activity - stopped working (1975 GT coupé).

I ran through all the diagnostics today. Earthed the two wires for the reserve light and gauge reading to confirm the the gauge in the dashboard was doing what it should; it was so the problem lied in the fuel sender.

I took it out, apart, cleaned it up, cleaned up all contacts with fine sandpaper and contact cleaner and for testing purposes made up a separate earth wire connecting the sender body to the rear light earthing point. This way I could fiddle with the float whilst looking at the gauge through the rear window. Success! Reserve light coming on when it should, gauge moving with the float.

Remove the homemade earth wire, put sender back in tank, not working any more. OK, perhaps it's the tank earth. So I put my homemade earth cable back on, still not working.

OK, take it out again. Homemade earth wire back on. Out of tank, doing what it should both for reserve light and gauge activity.

Put it back in the tank - without the screws this time, just physically placing it in the hole - nothing. Lift it out, reserve light comes on, fiddle with the float, gauge moves. Put it back in, nothing again. All whilst not touching any of the electrical connections. The tank has enough fuel in it that there ought to be a reading from the gauge.

I presume the structure of the tank is simply empty, not with obstacles that the float is meant to be passed over whilst reinserting? Is it possible it's touching something and staying in a middle ground position between when the reserve light goes off and when the needle starts to move? it doesn't even twitch when I put the ignition on.
 

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Discussion Starter #2
P.S. I'm discounting the possibility of a pierced float as it doesn't feel full of fuel when taken out, doesn't leak, and if it potentially was, then it would stay at the bottom and the reserve light would come on, which it doesn't.
 

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"Put it back in the tank - without the screws this time,". Gives a hint....
More then likely the screws are the ground path.
 

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Discussion Starter #4
OK, I did the opposite and chased up my theory - "Is it possible it's in a middle position between when the reserve light goes off and when the needle starts to move?"

That's exactly what it was. I checked with the gauge out again and sure enough the needle only moved after the point where the reserve light goes out, and the amount of fuel in my tank just happened to be somewhere about there. Added a jerrycan, got a reading.

I won't delete my post in the unlikely event somebody else ends up in the same scenario.
 

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Discussion Starter #5
"Put it back in the tank - without the screws this time,". Gives a hint....
More then likely the screws are the ground path.
They are. But I had a separate ground wire bolted to it.
 
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