If done correctly, and it is hard not to!!, they will be more reliable than ford wiring which can be up to 21 years old so does well anyway!!
If it were me I would run a new live wire/relay from the front to rear for the live, using original wire as trigger for said relay, then earth the pump inside the car somewhere at the rear as there is plenty of areas to get a good earth here, even if it means drilling a hole and using nut and bolt to hold terminal, as it can be easily hidden.
tabetha