I happen to know first hand from previous stupidity that it takes about 1 second to fry the 6 volt gauge. Maybe less. Its immediate and very painful.
Sounds like you are good to go!
Try this and let me know what you get...
If you have a 6v gauge, there is about 1.6 volts between the center terminal on the sender and ground. If you have a 12v gauge, there is about 2.8-3.2 volts. (these are full tank numbers, so reduce them by however much is in your tank).
