Edited: another fuel/temp gauge thread, but turns out the harness is melted together

Post 4 shows a graph of various senders and what MY gauge needs, resistance wise, to read correctly.

Product Review: A100 Fuel Sender For 67 Dart

When your tank has 40L (about 10 gallons) the sender should have about 20 to 25 ohms. When empty it should be in the 70 to 80 ohms.

It is posable that your gauges are damaged, I recently had my IVR fail and it pegged the temp and fuel gauges. Fuel seems to have survived but the temp reads off the chart low when the key is off and 1/2 way between cold and the first line of normal when at normal operating temp. (It used to be a few degrees to the right of the first line of the normal range)

Notice post 25, damaged gauge...

The gauge failure posts cursed my car