1. Have leak in fuel tank so removed the tank but how is the sender removed. Seems like a screwdriver on the cogged collar might work but nothing moves. Any suggestions?
2. Am switching from 6V pos ground to 12V neg ground. Do I need a 12V sender? Or will the existing one work??

 

Should be able to move remove the collar....

Sender should be ohm's if using the same gage.... Should be fine..