Found this site that references older GM gas gauges:
https://www.fillingstation.com/artic...ugetesting.htm
Newer ones, 60's until they went digital work the same but the ohms changed to 90. If your sender is 90 ohm but your gauge is expecting 30, the needle should move a little but won't do a full scale reading.
Simple description is one wire from gauge to sender and a second wire from body of sender to ground. Not sure when GM added the sender to frame grounds. Earlier years may have assumed the tank mounting system provided a ground.
General rules:
Never connect live power to sender wiring.
Max full all the time is open circuit/missing ground on sender wiring.
Empty all the time, short circuit in gauge to tank wiring.