What you are dealing with is called a female spade lug electrical connection. It is a slip on, friction fit connection. There will be no "click" when putting the wire terminal onto the male spade lug. There is a metal terminal inside of the red plastic outer covering to the terminal. With the female terminal pulled off of the male terminal on the sender just give the female terminal a light squeeze with some pliers on the narrow part of the red covering. Do not use too much force. Easy does it is the key word here. If you just pull the female terminal off of the sender's male part you can look into the female terminal and see how the metal part is made. Google "female spade lug terminal" and you'll see the two curved parts which need tightening up. Once squeezed, try re-inserting the female terminal onto the male terminal. You shouldn't have to use too much force and it should go on. That's all there is to it.

 

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