you have a few switches, in the pipework that you've found and there's another one in the drivers side wheel arch liner hidden away

it could also be that the drier has filled up and the gas can't gas any more and, in one of the pipes going from the wing through the arch and into the engine bay there is, for the want of a better word, a spring

this has been the cause of issues in the past on other cars as it stops the flow of gas

on mine i've had the pressure switch fault and the earth return from the pump clutch fault too so if it's the relay only then hang on and i'll post a link