So... the bits I can understand so far...

12Way Plug:

Pin 1 - Brown -
Pin 2 - Green - Connect to Escort Mk4 Tachometer
Pin 3 - Brown -
Pin 4 - Black - Connect to +12v Ignition Switch (with an inline fuse)
Pin 5 - Black/Red
Pin 6 - Red - Connect to +12v (with an inline fuse)
Pin 7 - Black -
Pin 8 - Black/Green -
Pin 9 - Brown/White -
Pin10 - Brown/Green -
Pin11 - Black/White -
Pin12 - Brown -

Anyone else care to add anything? Would like to hear from someone whose fitted a zetec using a Fiesta Si loom to confirm its going to work as I dont want to damage the ECU as they're pigs to find non-pats ones these days.