Fuel sender wiring

[caddycol]

Hi fellas and one have a wiring diagram to hand
trucks all ready for its mot but i just found out the fuel gauge dose not work

it has the original plug on the rear of the gauge with 2 wires in it but i found a wire on the floor attached to fresh air?

i traced it to the fuel tank so i have a earth of the tank to the body then this long wire just laying by the pedals
were it go chaps ??

thanks Col