i need to run a wire from the fuel pump to the ignition switch how do i do it

why dont you repair the damage to the harness?? it may be easier and the controls will be back with the pump. running this wire will activate the pump all the time with the key on. it is relay controlled because the draw is around 20 amps and that is a lot to add to the ignition switch.
I would look at repairing the harness than doing this bypass.

roy

how would i know which wire it is

ok, you apparently saw the damage from the rodent. where is the damage to the harness?? or are you just assuming??

Roy