Fuel sending unit/Fuel gauge not working

[diplomat 1]

I have a 90 300zx n/a. I recently put in a motor after the car sat for years before I got it (last inspection sticker was 2010). I put a motor in and got it running. I put in about 4 gallons of 93 gas but the needle stays on E. I am thinking it's either the gauge itself or the sending unit. Maybe since the car sat for so long the float device is stuck in the empty position? Well I would like to test and find out if it's either the sending unit or gauge and need advice on how to do it. Any help would be great thanks.

[DCaff300ZX]

My money is on a stuck float, not sure what to do about that other than I read advise awhile back regarding flushing the gas tank with diesel fuel, perhaps a soak and LIGHT tapping around the float area with a rubber mallet would release. Obviously you need to drain the diesel and refill with gas before use.
The online service manual would also have testing procedures for the tank sending unit, and can be found in the "everything you need to know about the Z32" sticky at the top of our Z32 page.

[diplomat 1]

So I ended up needing to not diagnose anything, well hopefully. I went to my fuel pump and it was rusted and slot of rust at that. The wires that are on the fuel sending unit on top just broke off like nothing due to corrosion so I figured it was cause of that. I also realized I had a fuel leak on top of the sending unit due to the rust so I ordered a pre owned sending unit as well as a new oring and am waiting on it in the mail. I know at not advisable to buy a used sending unit but money is tight. Hopefully it fixes both problems