CK,
Welcome to the Stovebolt. You have several things going on, so the answer isn't straight forward. The factory configuration for gauge and sender is just as 'Chev's' indicates. Gauge and sender must be matched at 0-30 ohms to read properly. Few other rigs ever had a 30 ohm system that I know of.
The only way your gauge will read properly is with a 0-30 ohm sending unit. Here is a basic test for gauge, wiring and sending unit health.
With the key ON, pull the wire at the sending unit. This should send the gauge to FULL. Leave the key ON and ground that sending unit wire to a clean, good ground. That should drive the gauge needle to EMPTY.
This means the gauge is working and the wire back to the sender is intact. You must make sure your tank is grounded and the gauge has a clean contact with the dash where it's bolted in.
As you can see from the test, if you pull the wire off the sending unit, turn the key ON and see the gauge swing to EMPTY, it's an indication you have a grounded spot in the wire somewhere...maybe mashed under a seat or piece of trim.
None of this jabber addresses the fact that anything other than a 0-30 ohm gauge and a 0-30 ohm sender will work together properly. They probably wouldn't be responsible for the activity you are seeing though, but more along the lines of a inaccurate reading. I hope this helps some...and welcome to the site.
Stuart
