Classic/Antique Car Repair: 1977 Ford Ranchero Fuel Gauge Stuck on Empty, 1977 ford ranchero, fuel gauge

Question
My father recently passed down his 1977 Ford Ranchero to me.  Everything runs great and last week, I noticed the fuel gauge said it was empty so I filled it up with gas and it is still indicating that there is no fuel.  It was working fine before and I have no idea where to start to resolve this issue.  Please help.  Thanks!

Answer
Hi John:
First the to do is just tap it lightly just to make
sure it isn't stuck at the dash. If you can't get it to move,
the it sound like you Fuel Sending Unit is either stuck or bad.

The Fuel Sending Unit is in the tank and it measures how much
fuel is in the tank.