The fuel sender is just a coil of resistive wire, with a wiper arm that makes contact. The fuel level lifts the float, which rotates the wiper arm, making it move along the coil so the resistance drops as the fuel level rises.
The wiper can eventually wear out and make poor or intermittent contact with the coil. You can make a temporary fix by bending the wiper arm so it makes better contact. (The temporary fix in my Delica has worked for about 5 years now...)
The wiper arm is inside a metal casing, and you need to gently un-bend the tabs that hold it together.
I suspect the fault is wear in the bushes that hold the float arm. This allows the float arm to move sideways, causing the wiper arm to lose contact with the resistive coil.
Before you modify anything, move the float arm up and down and listen to the sound of the wiper arm on the coil. It should make an even "zzzz" noise. If the noise goes quiet, that's where the contact is getting lighter. Bend the wiper arm a little to increase contact pressure, and listen again. It might take a few tries before you achieve reliable consistent contact. Once you think it's fixed and before reinstalling the sender(s), I would dry test the sender by plugging it in, turning on the ignition, and checking that the fuel gauge works properly.
While you have the sender out, also check that the float still floats.
The wiper can eventually wear out and make poor or intermittent contact with the coil. You can make a temporary fix by bending the wiper arm so it makes better contact. (The temporary fix in my Delica has worked for about 5 years now...)
The wiper arm is inside a metal casing, and you need to gently un-bend the tabs that hold it together.
I suspect the fault is wear in the bushes that hold the float arm. This allows the float arm to move sideways, causing the wiper arm to lose contact with the resistive coil.
Before you modify anything, move the float arm up and down and listen to the sound of the wiper arm on the coil. It should make an even "zzzz" noise. If the noise goes quiet, that's where the contact is getting lighter. Bend the wiper arm a little to increase contact pressure, and listen again. It might take a few tries before you achieve reliable consistent contact. Once you think it's fixed and before reinstalling the sender(s), I would dry test the sender by plugging it in, turning on the ignition, and checking that the fuel gauge works properly.
While you have the sender out, also check that the float still floats.