My Fuel Gauge in my FC3S doesn't work
 

I just purchased a second generation Rx7. It's not in the best of shapes, but I bought it as a project car and have big plans. Anyway, among the many cosmetic problems asscoiated with it, is the Fuel Gauge doesn't read how much fuel is in the tank. I didn't know this was wrong when i bought it, so me and a friend were at the gas station pumping 10 bucks worth of gas into a full tank. We started the car up and realized that it doesn't read. Anywho, I don't think i have to buy a new gauge or anything, and i don't want to take it to a mechanic if i can just fix it myself... any ideas?
Thanks in Advance

You in tank sender unit might be bad. Pull it and check it.