What size wire goes from the fuel pump relay. to the electric fuel pump.

14 ga. works fine. just make sure you use tinned multi-strand cunductor wire. and tinned solderless connectors . then cover with adhesive lined shrink tube. NO SOLDER. the multi strand carries the constant load better and has less resistance. some people go to 12 ga. typical copper thinking it's better because of size not realizing the lack of ability to carry constant load.

good luck