Fuel tank sender issues

The actual order of events is important here. When did you change the sender? Before or after you filled the tank with water? X2 on the replacement senders — they are "generic" and are not calibrated for the weird shape of the A-body tank. Best to use the original one if it is at all salvageable. But if it is suddenly not registering at all, it is probably because you forgot to replace the ground strap.