Saw this description in looking up engine wiring harness on parts site:

"Wiring harness to be used in conjunction with fuel level sending units on early models with round pin electrical connections."

What's the wiring harness have to do with the fuel level sending units? My fuel gauge goes up and down when the gas tank is just filled up. After 1/8 of the tank is used, the gauge is 100% normal. Any relationship?