I have just purchased a loom for this upgrade 2wd saph i,m under the understanding that the original earth from original relay either needs to be taped up or earthed to chassis. Then your loom you make or buy will have its earth which as said can go direct to batterie or body and pump earth. I had a good look at my cars wiring today and it seems straight forward being a novice. Keep your cut off switch in circuit as usual , on my car the original live going to the cut off switch goes direct to from here to + pump . On that part of the live wire (black/red) Is where you need to feed relay live (original pump live) on ur new relay pin 86 (ignition live). Earth/ground pin 85 , pin 30 is 12v fused direct from batt , pin 87 live to pump.

I do hope im right lol please correct me if not
edit- pin 85 earth ground ur choice , either to body or batterie

Mike