For anyone else wanting to use the stock GTST loom;
The resistor pack will have seven wires, 6 will all be the same and IIRC, one will be white.
The injector plugs (wiring to injector) should have two wires. One will be the 12v + (and each injectors 12v+ is the same colour wire), and one earth, switched via the ecu (which are different to the next colour wise).
You need to cut the 12v + wire to each injector say 3-4 inches from the plug.
Now get one of the wires from the resistor pack (the non white ones), one for each injector and attach it to the cut injector plug wire. It doesn't matter which of the 6 you connect to the injector plug as its the earth that is switched via the ecu.
Now, for me, I used the 6th cylinder 12v + (from the harness end) to give the resistor pack power.
Easier to use this pic for reference..