rorischagrin

Hey guys, so I bought this used 08 ford f150 that seems to have been sitting for a while (rusty). The fuel level sensor is not working properly and i'd rather not drop the tank unless it is definitely the sensor. When I first bought the truck the meter marked about 2/3rd and eventually the gas ran out and it still marked 2/3. When i filled the tank, it marked full and then wouldn't go down. Now it just marks empty even when its filled. It's definitely the sensor right? The truck is also pretty rusty, so could it be a bad wire?