You need a boggo std SPST, single pole single throw switching relay, these are the yellow ones ford uses and will have 85 86 87 and 30, or 30/51 markings.
Personally on the S1 S2 I would just also get a fuel pump cut off from a scrap mondy/escort etc, then wire direct from position 2 of the ignition switch to the relay switched supply(86), 30 is battery input through a fuse, 85 is earth, and 87 is the output from the relay to the pump, through a fuel cut off for safety.
Run your earth direct to the battery.
There are loads of threads on this under cossie fuel pump rewire, don't worry if the relay has both 87 and 87a, this just shows it to be a change over relay, will still work as before, depending on whether supplied(switched on) or not will determine which terminal the supply come outs of, 87 when un switched 87a when switched.
tabetha