Fuel sending unit bad?
 

So I bought this 85 rx7 from my g/fs uncle and got a great deal. I just got the fuel tank back from being boiled and sealed. The fuel gauge was contantly reading empy. Now I'm guessing the sending unit is shot but the 3 wires that connect to it are yellow, blue, and black. I tested all the wires with a test light and the yellow one has a pulsing light. And the other two are dead/ or have no power. Is this normal? Do I need to replace the sending unit. And can I install a new one after I reinstall the tank? I replaced all the screws too and had to drill out the old ones.

Thanks for any help in advance.