There are 3 wires that run the length of the tube.

Only the "low fuel" contact wire is actual copper. The others are NiCr resistance wire with a specific resistance per length. The slider moves up and down on these 2 wires creating a connection between them.

At the top of the tube there is a small amount of wire -> lower resistance -> higher voltage applied to the gauge.

At the bottom of the tube there is a larger amount of wire -> higher resistance -> lower voltage applied to the gauge.

Standard 22 or 24 ga copper will not work for these 2 wires, the gauge will just pin high all the time.

Best bet - visit a wrecking yard or eBay.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech