VAGCOM wiring (ABF)

Hey,
I'm trying to wire up the vagcom plug into my mk1 abf. I've been given a wiring diagram and the wires from my plug match the diagram except one. A yellow wire from the plug should go to a yellow wire on the ecu (pin 21) but there are no pure yellow wires on the ecu, and pin 21 is a grey/yellow one for the throttle closed switch. Some one must have wired this up correctly in the past. Please help.