Date registered: Jan 2011
Vehicle: 1978 406 w/ Eller hardtop
Location: Cincinnati, OH
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Fixed my fuel gauge-and here's how
After two years of checking my fuel level by looking in the tank...and by the even more definitive method I call "running out of fuel", I have made the fuel gauge work.
After carefully opening up the sending unit to expose the wirewound potentiometer inside, I re-soldered the connection of the super-thin potentiometer wire to the blue wire in photo.
Then I soldered the other end of the blue wire to the terminal at the top of the sending unit.
Last, I cleaned the contact surfaces of the potentiometer and the contact on the float arm with a spray electronics cleaner, and carefully re-assembled the sending unit.
Luckily for me, the one I have was held together by bent metal tabs--but yours may have rivets like hammogger mentioned.
Now, it reads 7/8 when it is COMPLETELY full, and reads 1/8 when it is 1/4 full. A bit pessimistic, but it totally works for me.
It might be possible to get more accuracy with cleaner terminals, or with some sort of tuning pot added to the system...but I don't think I'll bother.