gas tank sending connector

i just got a new gas tank and sending unit for my el camino. i took the wire and small connector from the old tank and sender and want to use it on the new one. (spectra FG91B), it doesn't seem to want to go on. its a strange connector, like a button and goes on to the small post of the sender. i looked on the spectra website and they don'tmention the need to buy a special wire to connect to the new sender so i am guessing i can still use the old one. is that true?

thanks