2005 FLSTN- FLSTNI Softail Deluxe: 2005 fuel gauge doesn't work...

Your bike has a 12 Volt 18 AH battery.

if you are fuel injected I would have to say fuel pressure regulator housing has broken

I think you're correct in your assumption. It may read differently but is it accurate? That's the question. Since the sending unit is so difficult to get into the tank. sometimes the arm gets bent resulting in an erronous reading. You can try bending the arm but it may take several trys to get it as close as you'd like.

Good Luck
Steve

F means it has overhead valve "big v-twin"
L means wide front tire
ST-Softail like you thought
N-Nostalgia like you thought
I means fuel injected (they used to offer with a carb)

hope that helps

Replace the sender unit in the tank