I'm guessing you have the main loom to connect to the ECU (1J0 971 425 A)
Not sure which other you need loom you need for cars that are not prewired (1J0 971 425 B and/or 1J0 971 425 C).
There might be someone on here that has the old wires that came part of a kit that they didn't use as their car were pre wired.
My car is a TDI which was already prewired to the ECU but did require a loom to the main cable socket box under the wiper motor.
You could always ask your local dealer for info on what loom is needed.