Fuel Sending Units and A-Body Fuel Tank Map

Trying to figure out what to do to make my fuel gauge work, at least showing Full when full and Empty when it's got a gallon or 2 in it.

Would appreciate if any experts could help me with a few questions and perhaps suggestions.

My Dart has the original OEM Fuel Gauge at dash and I still have the OEM sending unit that had a fatal corrosion problem at the middle of the steel tube due to our ridiculously bad gas around here. Now I am reviving the Dart and had to replace it with a new aftermarket sending unit that never gave a correct reading, most of the time it reads empty as if there is a bad connection or unplugged something.

I had to replace the gas tank due to corrosion too, using a plastic tank available here, which requires sending unit tube bending adjustments to reach bottom (it was 2" far from bottom) and also float adjustments.

Can I make readings playing with the send unit outside the tank? Did that for a while and melted the plastic plate that holds the resistance wire in the sending unit...

What I am curious about is if there is anything between the sender unit and the reader at the dash, it seems to be something (from factory) added to the instrument cluster and connected to the temp and gas gauges at the dash, as shown on pics, any idea what that is and what it does?
Thanks for any input.




View attachment 1715320010

View attachment 1715320011

View attachment 1715320016