Soooooooooo,
When you ohm tested the sender, you ohm'd between two points...... a: the sender's signal (pink?) wire and b: a ground wire.
Questions: With power OFF...
First thou, make sure it's off!! Have you measured to make sure there is not power on any of the gauges's connecting posts when you say it's off? You say when off, the needle is at 1/4? That's a tad strange unless the needle rests there when dead eh?
So, with the key off and the meter's negative lead on your battery's negative post, measure with the meter's positive lead for voltage on all the gauge's connecting post
If all is 0V then........I guess it rests there when dead.
So moving on,
1) Like the sender's signal (pink?) "a" wire, does the ground wire "b" you used in the above ohm test go directly to the tank as well?
2) If yes(or maybe) to "1", can you ohm test between that ground wire "b" you used in the above ohm test and your battery's negative post?
3) What is the resistance measurement?
If it's open'ish, the tank/sender's signal return is floating and needs grounding to main ground.
